SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES

12 Months Ended

Dec. 31, 2018

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES [abstract]

Disclosure of summary of significant accounting policies

3. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES

Basis of preparation

These consolidated financial statements have been prepared under the historical cost convention, except for as detailed in the accounting policies notes hereafter. These consolidated financial statements are presented in Renminbi ("RMB") and all values are rounded to the nearest million except when otherwise indicated.

Basis of consolidation

The consolidated financial statements include the financial statements of the Company and its subsidiaries for the year ended December 31, 2018.

The results of subsidiaries are consolidated from the date of acquisition, being the date on which the Group obtains control, and continue to be consolidated until the date that such control ceases. The financial statements of the subsidiaries are prepared for the same reporting period as the parent company, using consistent accounting policies.

The results of subsidiaries are included in the Company's statement of profit or loss and other comprehensive income to the extent of dividends received and receivable. The Company's interests in subsidiaries are stated at cost less any impairment losses.

All intra-group balances, income and expenses, unrealized gains and losses and dividends resulting from intra-group transactions are eliminated in full.

Business combinations and goodwill

Business combinations, other than business combinations under common control, are accounted for using the acquisition method. The consideration transferred is measured at acquisition date fair value which is the sum of the acquisition date fair values of assets transferred by the Group, liabilities assumed by the Group from the former owners of the acquiree and the equity interests issued by the Group in exchange for control of the acquiree. For each business combination, the Group elects whether it measures the non-controlling interests in the acquiree either at fair value or at the proportionate share of the acquiree's identifiable net assets. All other components of non-controlling interests are measured at fair value. Acquisition related costs incurred are included in profit or loss.

When the Group acquires a business, it assesses the financial assets acquired and financial liabilities assumed for appropriate classification and designation in accordance with the contractual terms, economic circumstances and pertinent conditions as at the acquisition date. This includes the separation of embedded derivatives in host contracts by the acquiree.

If the business combination is achieved in stages, the Group's previously held equity interest in the acquiree is remeasured to fair value at the acquisition date through profit or loss or other comprehensive income, as appropriate.

Any contingent consideration to be transferred by the acquirer is recognized at fair value at the acquisition date. Contingent consideration that is classified as equity is not remeasured at subsequent reporting dates and its subsequent settlement is accounted for within equity. Contingent consideration that is classified as an asset or a liability is remeasured to fair value at subsequent reporting dates, with the corresponding gain or loss being recognized in profit or loss.

Goodwill is initially measured at cost, being the excess of the aggregate of the purchase consideration, the amount recognized for non-controlling interests and any fair value of the Group's previously held equity interests in the acquiree over the identifiable net assets acquired and liabilities assumed. If the sum of this consideration and other items is lower than the fair value of the net assets of the business acquired, the difference is recognized in profit or loss as a gain on bargain purchase.

 After initial recognition, goodwill is measured at cost less any accumulated impairment losses. Goodwill is tested for impairment annually or more frequently if events or changes in circumstances indicate that the carrying value may be impaired. For goodwill arising on an acquisition in a reporting period, the cash-generating unit (or group of cash-generating units) to which goodwill has been allocated is tested for impairment before the end of that reporting period.

For the purposes of impairment testing, goodwill is allocated to each of the Group's cash-generating units (or group of cash- generating units) that is expected to benefit from the synergies of the combination, which represent the lowest level at which the goodwill is monitored for internal management purposes and not larger than an operating segment.

Impairment is determined by assessing the recoverable amount of the exploration and production ("E&P") segment, using value in use, to which the goodwill relates. Where the recoverable amount of the cash-generating unit (or group of cash-generating units) is less than the carrying amount, an impairment loss on goodwill is recognized. An impairment loss recognized for goodwill is not reversed in a subsequent period.

Where goodwill has been allocated to a cash-generating unit (or group of cash-generating units) and part of the operation within that unit is disposed of, the goodwill associated with the operation disposed of is included in the carrying amount of the operation when determining the gain or loss on the disposal. Goodwill disposed of in these circumstances is measured based on the relative value of the operation disposed of and the portion of the cash-generating unit (or group of cash-generating units) retained.

Subsidiaries

Subsidiaries are all those entities over which the Group has power over the investee such that the Group is able to direct the relevant activities, has exposure or rights to variable returns from its involvement with the investee and has the ability to use its power over the investee to affect the amount of the investor's returns.

Associates

Based on the Group's ownership percentage (considering its direct ownership as well as potentially exercisable or convertible shares) and other contractual terms, the Group has significant influence over its associates, rather than the power to control.

The Group's investments in associates are stated in the consolidated statement of financial position at the Group's share of net assets under the equity method of accounting, less any impairment losses. Necessary adjustments are made to bring into line any dissimilar accounting policies that may exist. Under the equity method, an investment in an associate is initially recognized in the consolidated statement of financial position at cost and adjusted thereafter to recognize the Group's share of the profit or loss and other comprehensive income of the associate. Unrealized gains and losses resulting from transactions between the Group and its associates are eliminated to the extent of the Group's investments in the associates, except where unrealized losses provide evidence of an impairment of the asset transferred. Goodwill arising from the acquisition of associates is included as part of the Group's investments in associates and is not individually tested for impairment.

Joint arrangements

Certain of the Group's activities are conducted through joint arrangements. Joint arrangements are classified as either a joint operation or joint venture, based on the rights and obligations arising from the contractual obligations between the parties to the arrangement.

 Joint control

Joint control is the contractually agreed sharing of control of an arrangement, which exists only when decisions about the relevant activities require unanimous consent of the parties sharing control.

Joint operations

Some arrangements have been assessed by the Group as joint operations as both parties to the contract are responsible for the assets and obligations in proportion to their respective interest, whether or not the arrangement is structured through a separate vehicle. This evaluation applies to both the Group's interests in production sharing arrangements and certain joint operation.

The Group entered into numerous production sharing arrangements or similar agreements in China and overseas countries. The Group's participating interest may vary in each arrangement. The Group, as one of the title owners under certain exploration and/or production licenses or permits, is required to bear exploration (with some exceptions in China), development and operating costs together with other co-owners based on each owner's participating interest. Once production occurs, a certain percentage of the annual production or revenue is first distributed to the local government, which, in most cases, with the nature of royalty and other taxes or expenses, and the rest of the annual production or revenue is allocated among the co-owners.

The Group accounts for the assets, liabilities, revenues and expenses relating to its interest in a joint operation in accordance with the IFRSs/HKFRSs applicable to the particular assets, liabilities, revenues and expenses.

Joint venture

A joint venture is a joint arrangement whereby the parties that have joint control of the arrangement have rights to the net assets of the arrangement.

The Group's investments in joint ventures are stated in the consolidated statement of financial position at the Group's share of net assets under the equity method of accounting, less any impairment losses. Necessary adjustments are made to bring into line any dissimilar accounting policies that may exist. Under the equity method, an investment in a joint venture is initially recognized in the consolidated statement of financial position at cost and adjusted thereafter to recognize the Group's share of the profit or loss and other comprehensive income of the joint venture. Where the profit sharing ratios are different to the Group's equity interest, the share of post-acquisition results of the joint ventures is determined based on the agreed profit sharing ratio. Unrealized gains and losses resulting from transactions between the Group and its joint ventures are eliminated to the extent of the Group's investments in the joint ventures, except where unrealized losses provide evidence of an impairment of the asset transferred. Goodwill arising from the acquisition of joint ventures is included as part of the Group's investments in joint ventures and is not individually tested for impairment.

Related parties

A party is considered to be related to the Group if:

(a) the party is a person or a close member of that person's family and that person

(i) has control or joint control of the Group;

(ii) has significant influence over the Group; or

(iii) is a member of the key management personnel of the Group or of a parent of the Group;

(b) the party is an entity where any of the following conditions applies:

(i) the entity and the Group are members of the same group;

(ii) one entity is an associate or joint venture of the other entity (or of a parent, subsidiary or fellow subsidiary of the other entity);

(iii) the entity and the Group are joint ventures of the same third party;

(iv) one entity is a joint venture of a third entity and the other entity is an associate of the third entity;

(v) the entity is a post-employment benefit plan for the benefit of employees of either the Group or an entity related to the Group;

(vi) the entity is controlled or jointly controlled by a person identified in (a);

(vii) a person identified in (a)(i) has significant influence over the entity or is a member of the key management personnel of the entity (or of a parent of the entity); and

(viii) the entity, or any member of a group of which it is a part, provides key management personnel services to the Company or to the parent of the Company.

Impairment of non-financial assets other than goodwill

Where an indication of impairment exists, or when annual impairment testing for an asset is required (other than inventories, deferred tax assets, financial assets and goodwill), the asset's recoverable amount is estimated. An asset's recoverable amount is the higher of the asset's or cash-generating unit's value in use and its fair value less costs of disposal, and is determined for an individual asset, unless the asset does not generate cash inflows that are largely independent of those from other assets or groups of assets, in which case the recoverable amount is determined for the cash-generating unit to which the asset belongs.

An impairment loss is recognized only if the carrying amount of an asset exceeds its recoverable amount. In assessing value in use, the estimated future cash flows are discounted to their present value using a pre-tax discount rate that reflects current market assessments of the time value of money and the risks specific to the asset. An impairment loss is charged to profit or loss in the period in which it arises in those expense categories consistent with the function of the impaired asset.

An assessment is made at the end of each reporting period as to whether there is any indication that previously recognized impairment losses may no longer exist or may have decreased. If such an indication exists, the recoverable amount is estimated. A previously recognized impairment loss of an asset other than goodwill is reversed only if there has been a change in the estimates used to determine the recoverable amount of that asset, but not to an amount higher than the carrying amount that would have been determined (net of any depreciation/amortization) had no impairment loss been recognized for the asset in prior years. A reversal of such an impairment loss is credited to profit or loss in the period in which it arises.

Property, plant and equipment

Property, plant and equipment comprise oil and gas properties, and vehicles and office equipment and others.

(a) Oil and gas properties

For oil and gas properties, the successful efforts method of accounting is adopted. The Group capitalizes the initial acquisition costs of oil and gas properties. Impairment of initial acquisition costs is recognized based on exploratory experience and management judgement and charged to profit and loss as exploration expenses. Upon discovery of commercial reserves, acquisition costs are transferred to proved properties. The costs of drilling and equipping successful exploratory wells, all development expenditures on construction, installation or completion of infrastructure facilities such as platforms, pipelines, processing plants and the drilling of development wells and the building of enhanced recovery facilities, including those renewals and betterments that extend the economic lives of the assets, and the related borrowing costs are capitalized. The costs of unsuccessful exploratory wells and all other exploration costs are expensed as incurred.

The Group carries exploratory well costs as an asset when the well has found a sufficient quantity of reserves to justify its completion as a producing well and where the Group is making sufficient progress assessing the reserves and the economic and operating viability of the project. Exploratory well costs not meeting these criteria are charged to expenses. Exploratory wells that discover potentially economic reserves in areas where major capital expenditure will be required before production would begin and when the major capital expenditure depends upon the successful completion of further exploratory work remain capitalized and are reviewed periodically for impairment.

Producing oil and gas properties are depreciated on a unit-of-production basis over the proved developed reserves. Common facilities that are built specifically to service production directly attributed to designated oil and gas properties are depreciated based on the proved developed reserves of the respective oil and gas properties on a pro-rata basis. Common facilities that are not built specifically to service identified oil and gas properties are depreciated using the straight-line method over their estimated useful lives. Costs associated with significant development projects are not depreciated until commercial production commences and the reserves related to those costs are excluded from the calculation of depreciation.

Capitalized acquisition costs of proved properties are depreciated on a unit-of-production method over the total proved reserves of the relevant oil and gas properties.

(b) Vehicles, office equipment and others

Vehicles, office equipment and others are stated at cost less accumulated depreciation and impairment losses. The straight-line method is adopted to depreciate the cost less any estimated residual value of these assets over their expected useful lives. The useful lives of vehicles, office equipment and other assets are in line with their beneficial periods.

Where parts of an item of property, plant and equipment have different useful lives, the cost of that item is allocated on a recoverable basis among the parts and each part is depreciated separately.

Residual values, useful lives and the depreciation method are reviewed and, adjusted if appropriate, at each reporting date.

Any gains and losses on disposals of property, plant and equipment (calculated as the difference between the net disposal proceeds and the carrying amount of the asset) are recognized in profit or loss.

Intangible assets other than goodwill

The intangible assets of the Group comprise software and others, gas processing rights under NWS Project, marketing transportation and storage contracts, drilling rig contracts and seismic data usage rights. Intangible assets with finite lives are carried at cost, less accumulated amortization and accumulated impairment losses. The cost of intangible assets acquired in a business combination is the fair value as at the date of acquisition. Intangible assets with finite lives except for gas processing rights, are amortized on the straight-line basis over the useful economic life and assessed for impairment whenever there is an indication that the intangible asset may be impaired. The amortization period and the amortization method for an intangible asset with a finite useful life are reviewed at least at each financial year end.

The intangible assets regarding software have been amortized on the straight-line basis over their respective useful lives. The intangible asset regarding the gas processing rights has been amortized upon the commercial production of the liquefied natural gas on a unit-of-production basis over the total proved reserves of the relevant asset. The intangible assets regarding the marketing transportation and storage contracts and drilling rig contracts are amortized over the life of the contracts on the straight-line basis. The intangible assets related to the seismic data usage rights are amortized over the estimated useful life of the seismic data.

Major maintenance and repairs

Expenditure on major maintenance refits and repairs comprises the costs of replacement assets or parts of assets and overhaul costs. Where an asset or part of an asset that is separately depreciated and is replaced, and it is probable that future economic benefits associated with the item will flow to the Group, the replacement expenditure is capitalized. Where part of the asset is not separately considered as a component, the replacement value is used to estimate the carrying amount of the replaced assets which is immediately written off. All other maintenance costs are expensed as incurred.

Research and development costs

All research costs are expensed as incurred.

Expenditure (other than that relating to oil and gas properties discussed above) incurred on projects to develop new products is capitalized and deferred only when the Group can demonstrate the technical feasibility of completing the intangible asset so that it will be available for use or sale, its intention to complete and its ability to use or sell the asset, how the asset will generate future economic benefits, the availability of resources to complete the project and the ability to measure reliably the expenditure during the development. Product development expenditure which does not meet these criteria is expensed when incurred.

Financial assets

Financial assets are initially measured at fair value except for trade receivables arising from contracts with customers which are initially measured in accordance with IFRS 15/HKFRS 15 since January 1, 2018. All recognized financial assets are subsequently measured in their entirety at either amortized cost or fair value, depending on the classification of the financial assets.

(a) Financial assets at amortized cost

Debt instruments and hybrid contracts that meet the following conditions are subsequently measured at amortized cost less impairment loss:

• the asset is held within a business model whose objective is to hold assets in order to collect contractual cash flows; and

• the contractual terms of the instrument give rise on specified dates to cash flows that are solely payments of principal and interest on the principal amount outstanding.

All other financial assets are subsequently measured at fair value.

The effective interest method is a method of calculating the amortized cost of a financial asset or financial liability and of allocating interest income and interest expense over the relevant period. The effective interest rate is the rate that accurately discounts estimated future cash receipts and payments (including all fees and points paid or received that form an integral part of the effective interest rate, transaction costs and other premiums or discounts) through the expected life of the financial asset or financial liability, or, where appropriate, a shorter period, to the net carrying amount on initial recognition.

(b) Financial assets at fair value through other comprehensive income (FVTOCI)

On initial recognition, the Group can make an irrevocable election (on an instrument-by-instrument basis) to designate investments in equity instruments as at FVTOCI. The Group has investments in certain equity instruments (publicly traded or non-publicly traded), the purpose of which are not held for trading, but held for medium or long-term strategic purpose. Therefore, those investments in equity instruments are designated as at FVTOCI.

Investments in equity instruments at FVTOCI are initially measured at fair value plus transaction costs. Subsequently, they are measured at fair value with gains or losses arising from changes in fair value recognized in other comprehensive income and accumulated in other reserves. The cumulative gain or loss will not be reclassified to profit or loss on disposal of the investments.

Dividends from these investments in equity instruments are recognized in profit or loss when the Group's right to receive the dividends is established, unless the dividends clearly represent a recovery of part of the cost of the investment.

(c) Financial assets at fair value through profit or loss (FVTPL)

Financial assets that do not meet the criteria for being measured at amortized cost or FVTOCI or designated as at FVTOCI are measured at FVTPL.

Financial assets at FVTPL are measured at fair value at the end of each reporting period, with any gains or losses arising on remeasurement recognized in profit or loss.

Fair value

The fair value of financial instruments that are traded in active markets at each reporting date is determined by reference to quoted market prices or dealer price quotations, without any deduction for transaction costs.

For financial instruments not traded in an active market, the fair value is determined using appropriate valuation techniques. Such techniques may include using recent arm's length market transactions; reference to the current fair value of another instrument that is substantially the same; a discounted cash flow analysis or other valuation models.

An analysis of fair values of financial instruments and further details as to how they are measured are provided in note 33.

Impairment of financial assets

Impairment of financial assets on and after January 1, 2018

The Group recognizes a loss allowance for ECL on financial assets which are subject to impairment under IFRS 9/HKFRS 9 (including cash and cash equivalents, time deposits with maturity over three months, trade receivables and other receivables). The amount of ECL is updated at each reporting date to reflect changes in credit risk since initial recognition.

Lifetime ECL represents the ECL that will result from all possible default events over the expected life of the relevant instrument. In contrast, 12-month ECL ("12m ECL") represents the portion of lifetime ECL that is expected to result from default events that are possible within 12 months after the reporting date. Assessment is done based on the Group's historical credit loss experience, adjusted for factors that are specific to the debtors, general economic conditions and an assessment of both the current conditions at the reporting date as well as the forecast of future conditions.

The Group always recognizes lifetime ECL for trade receivables without significant financing component.

For all other instruments, the Group measures the loss allowance equal to 12m ECL, unless when there has been a significant increase in credit risk since initial recognition, in which case the Group recognizes lifetime ECL. The assessment of whether lifetime ECL should be recognized is based on significant increases in the likelihood or risk of a default occurring since initial recognition.

Significant increase in credit risk

In assessing whether the credit risk has increased significantly since initial recognition, the Group compares the risk of a default occurring on the financial instrument as at the reporting date with the risk of a default occurring on the financial instrument as at the date of initial recognition. In making this assessment, the Group considers both quantitative and qualitative information that is reasonable and supportable, including historical experience and forward-looking information that is available without undue cost or effort.

In particular, the following information is taken into account when assessing whether credit risk has increased significantly:

· an actual or expected significant deterioration in the financial instrument's external (if available) or internal credit rating;

· significant deterioration in external market indicators of credit risk, e.g. a significant increase in the credit spread, the credit default swap prices for the debtor;

· existing or forecast adverse changes in business, financial or economic conditions that are expected to cause a significant decrease in the debtor's ability to meet its debt obligations;

· an actual or expected significant deterioration in the operating results of the debtor;

· an actual or expected significant adverse change in the regulatory, economic, or technological environment of the debtor that results in a significant decrease in the debtor's ability to meet its debt obligations.

Irrespective of the outcome of the above assessment, the Group presumes that the credit risk has increased significantly since initial recognition when contractual payments are more than 30 days past due, unless the Group has reasonable and supportable information that demonstrates otherwise.

The Group regularly monitors the effectiveness of the criteria used to identify whether there has been a significant increase in credit risk and revises them as appropriate to ensure that the criteria are capable of identifying significant increase in credit risk before the amount becomes past due.

Definition of default

For internal credit risk management, the Group considers an event of default occurs when information developed internally or obtained from external sources indicates that the debtor is unlikely to pay its creditors, including the Group, in full (without taking into account any collaterals held by the Group).

Credit-impaired financial assets

A financial asset is credit-impaired when one or more events of default that have a detrimental impact on the estimated future cash flows of that financial asset have occurred. Evidence that a financial asset is credit-impaired includes observable data about the following events:

· significant financial difficulty of the issuer or the borrower;

· a breach of contract, such as a default or past due event;

· the lenders of the borrower, for economic or contractual reasons relating to the borrower's financial difficulty, having granted to the borrower a concession that the lenders would not otherwise consider;

· it is becoming probable that the borrower will enter bankruptcy or other financial reorganization; or

· the disappearance of an active market for that financial asset because of financial difficulties.

Write-off policy

The Group writes off a financial asset when there is information indicating that the counterparty is in severe financial difficulty and there is no realistic prospect of recovery. Financial assets written off may still be subject to enforcement activities under the Group's recovery procedures, taking into account legal advice where appropriate. A write-off constitutes a derecognition event. Any subsequent recoveries are recognized in profit or loss.

Measurement and recognition of ECL

The measurement of ECL is a function of the probability of default, loss given default (i.e. the magnitude of the loss if there is a default) and the exposure at default. The assessment of the probability of default and loss given default is based on historical data adjusted by forward-looking information. Estimation of ECL reflects an unbiased and probability-weighted amount that is determined with the respective risks of default occurring as the weights.

Generally, the ECL is the difference between all contractual cash flows that are due to the Group in accordance with the contract and all the cash flows that the Group expects to receive, discounted at the effective interest rate determined at initial recognition.

Except for investments in debt instruments that are measured at FVTOCI, the Group recognizes an impairment gain or loss in profit or loss for all financial instruments by adjusting their carrying amount, with the exception of trade receivables and other receivables where the corresponding adjustment is recognized through a loss allowance account. For investments in debt instruments that are measured at FVTOCI, the loss allowance is recognized in OCI and accumulated in the FVTOCI reserve without reducing the carrying amount of these debt instruments.  

Impairment of financial assets prior to January 1, 2018

The Group assesses at each reporting date whether there is any objective evidence that a financial asset, other than those at FVTPL and FVTOCI, or a group of financial assets may be impaired.

In relation to trade and other receivables, a provision for impairment is made when there is objective evidence (such as the probability of insolvency or significant financial difficulties of the debtor and significant changes in the technological, market, economic or legal environment that have an adverse effect on the debtor) that the Group will not be able to collect all of the amounts due under the original terms of an invoice.

If there is objective evidence that an impairment loss on financial assets measured at amortized cost has been incurred, the amount of the loss is measured as the difference between the asset's carrying amount and the present value of estimated future cash flows (excluding future credit losses that have not been incurred) discounted at the financial asset's original effective interest rate (the effective interest rate computed at initial recognition). The carrying amount of the asset is reduced either directly or through the use of an allowance account. The amount of the impairment loss is recognized in profit or loss.

If, in a subsequent year, the amount of the estimated impairment loss decreases and the decrease can be related objectively to an event occurring after the impairment was recognized, the previously recognized impairment loss is reduced either directly or by adjusting the allowance account. Any subsequent reversal of an impairment loss is recognized in profit or loss, to the extent that the carrying value of the asset does not exceed amortized cost at the reversal date.

Derecognition of financial assets

A financial asset (or, where applicable a part of a financial asset or part of a group of similar financial assets) is derecognized when:

· The contractual rights to receive cash flows from the asset have expired; or

· the Group has transferred its rights to receive cash flows from the asset, or the Group retains the contractual rights to receive the cash flows from the asset, but has assumed an obligation to pay the received cash flows in full without material delay to a third party under a "pass-through" arrangement; and either (a) has transferred substantially all the risks and rewards of the asset, or (b) has neither transferred nor retained substantially all the risks and rewards of the asset, but has no control of the asset.

When the Group has transferred its rights to receive cash flows from an asset or has entered into a pass-through arrangement, it evaluates if and to what extent it has retained the risk and rewards of ownership of the asset. When it has neither transferred nor retained substantially all the risks and rewards of the asset nor transferred control of the asset, the Group continues to recognize the transferred asset to the extent of the Group's continuing involvement. In that case, the Group also recognizes an associated liability. The transferred asset and the associated liability are measured on a basis that reflects the rights and obligations that the Group has retained.

Financial liabilities at amortized cost (including interest-bearing loans and borrowings)

Financial liabilities including trade and accrued payables, other payables and accrued liabilities, and interest-bearing loans and borrowings are initially stated at fair value less directly attributable transaction costs and are subsequently measured at amortized cost, using the effective interest method.

Gains and losses are recognized in profit or loss when the liabilities are derecognized as well as through the amortization process.

Derecognition of financial liabilities

Financial liabilities are derecognized when the obligations under the liabilities are discharged, cancelled, or have expired.

When an existing financial liability is replaced by another from the same lender on substantially different terms, or the terms of an existing liability are substantially modified, such an exchange or modification is treated as a derecognition of the original liability and a recognition of a new liability, and the difference between the respective carrying amounts is recognized in profit or loss.

Offsetting of financial instruments

Financial assets and liabilities are offset and the net amount reported in the consolidated statement of financial position, if and only if, there is a currently enforceable legal right to offset the recognized amounts and there is an intention to settle on a net basis, or to realize the assets and settle the liabilities simultaneously.

Inventories and supplies

Inventories primarily consist of oil and supplies, including items for repairs and maintenance of oil and gas properties. Inventories are stated at the lower of cost and net realizable value. Costs of inventories and supplies represent purchase or production cost of goods and are determined on a weighted average basis.

Cash and cash equivalents

Cash and cash equivalents comprise cash at banks and on hand and short term deposits with an original maturity of three months or less.

Provisions

(a) General

A provision is recognized when a present obligation (legal or constructive) has arisen as a result of a past event and it is probable that a future outflow of resources will be required to settle the obligation, provided that a reliable estimate can be made of the amount of the obligation. When the effect of discounting is material, the amount recognized for a provision is the present value at the reporting date of the future expenditures expected to be required to settle the obligation. The increase in the discounted present value amount arising from the passage of time is included in profit or loss.

(b) Dismantlement liability

Dismantlement liability is recognized when the Group has a present legal or constructive obligation as a result of the past events, and it is probable that an outflow of resources will be required to settle the obligation, and a reliable estimate of the amount of the obligation can be made. A corresponding amount equivalent to the provision is also recognized as part of the cost of the related property, plant and equipment. The amount recognized is the estimated cost of dismantlement, discounted to its present value using a current pre-tax rate that reflects, where appropriate, the risks specific to the liability. Changes in the estimated timing of dismantlement or dismantlement cost estimates are dealt with prospectively by recording an adjustment to the provision, and a corresponding adjustment to property, plant and equipment. The unwinding of the discount on the dismantlement provision is included as a finance cost.

Income tax

Income tax comprises current and deferred tax. Income tax is recognized in the consolidated statement of profit or loss and other comprehensive income, either as an expense as it relates to operating activities or as a component of the applicable categories of other comprehensive income or expense.

Current tax assets and liabilities for the current and prior periods are measured at the amount expected to be recovered from or paid to the taxation authorities. The tax rates and tax laws used to compute the amount are those that are enacted or substantially enacted, by the reporting date, in the countries where the Group operates and generates taxable income.

Deferred tax is provided, using the balance sheet liability method, on all temporary differences at the reporting date between the tax bases of assets and liabilities and their carrying amounts for financial reporting purposes.

Deferred tax liabilities are recognized for all taxable temporary differences, except:

· when the deferred tax liability arises from the initial recognition of an asset or liability in a transaction that is not a business combination and, at the time of the transaction, affects neither the accounting profit nor taxable profit or loss; and

· in respect of taxable temporary differences associated with investments in subsidiaries, associates and interests in joint ventures, when the timing of the reversal of the temporary differences can be controlled and it is probable that the temporary differences will not reverse in the foreseeable future.

Deferred tax assets are recognized for all deductible temporary differences, the carryforward of unused tax credits and any unused tax losses to the extent that it is probable that taxable profit and taxable temporary differences will be available against which the deductible temporary differences, the carryforward of unused tax credits and unused tax losses can be utilized, except:

· when the deferred tax assets relating to the deductible temporary differences arise from the initial recognition of an asset or liability in a transaction that is not a business combination and, at the time of the transaction, affects neither the accounting profit nor taxable profit or loss; and

· in respect of deductible temporary differences associated with investments in subsidiaries, associates and interests in joint ventures, deferred tax assets are only recognized to the extent that it is probable that the temporary differences will reverse in the foreseeable future and taxable profit will be available against which the temporary differences can be utilized.

The carrying amount of deferred tax assets is reviewed at each reporting date and reduced to the extent that it is no longer probable that sufficient taxable profit will be available to allow all or part of the deferred tax asset to be utilized. Unrecognized deferred tax assets are reassessed at each reporting date and are recognized to the extent that it is probable that sufficient taxable profit and taxable temporary differences will be available to allow all or part of the deferred tax asset to be utilized.

Deferred tax assets and liabilities are measured at the tax rates that are expected to apply to the period when the asset is realized or the liability is settled, based on tax rates (and tax laws) that have been enacted or substantively enacted at the reporting date.

Deferred tax assets and deferred tax liabilities are offset if a legally enforceable right exists to set off current tax assets against current tax liabilities and the deferred taxes relate to the same taxable entity and the same taxation authority.

Revenue

Revenue from contracts with customers on and after January 1, 2018

Under IFRS 15/HKFRS 15, the Group recognizes revenue when (or as) a performance obligation is satisfied, i.e. when "control" of the goods or services underlying the particular obligation is transferred to the customer.

A performance obligation represents a good or service (or a bundle of goods or services) that is distinct or a series of distinct goods or services that are substantially the same.

Control is transferred over time and revenue is recognized over time by reference to the progress towards complete satisfaction of the relevant performance obligation if any one of the following criteria is met:

(1) the customer simultaneously receives and consumes the benefits provided by the Group's performance as the Group performs;

(2) the Group's performance creates and enhances an asset that the customer controls as the Group performs; or

(3) the Group's performance does not create an asset with an alternative use to the Group and the Group has an enforceable right to payment for performance completed to date.

Otherwise, revenue is recognized at a point in time when the customer obtains control of the distinct good or service.

A contract liability represents the Group's obligation to transfer goods or services to a customer for which the Group has received consideration (or an amount of consideration is due) from the customer.

Revenue recognition prior to January 1, 2018

Revenue is recognized when it is probable that the economic benefits will flow to the Group and when the revenue can be measured reliably, on the following bases:

(a) Oil and gas sales

Oil and gas sales represent the invoiced value of sales of oil and gas attributable to the interests of the Group, net of royalties, obligations to governments and other mineral interest owners. Revenue from the sale of oil and gas is recognized when the significant risks and rewards of ownership have been transferred, which is when title passes to the customer. Revenue from the production of oil and gas in which the Group has a joint interest with other producers is recognized based on the Group's working interest and the terms of the relevant production sharing contracts. Differences between production sold and the Group's share of production are not significant.

Oil and gas lifted and sold by the Group above or below the Group's participating interests in the production sharing contracts results in overlifts and underlifts. The Group records these transactions in accordance with the entitlement method under which overlifts are recorded as liabilities and underlifts are recorded as assets at year-end oil prices. Settlement will be in kind or in cash when the liftings are equalized or in cash when production ceases.

The Group has entered into gas sale contracts with customers, which contain take-or-pay clauses. Under these contracts, the Group makes a long term supply commitment in return for a commitment from the buyer to pay for minimum quantities, whether or not it takes delivery. These commitments contain protective (force majeure) and adjustment provisions. If a buyer has a right to get a "make up" delivery at a later date, revenue recognition is deferred. If no such option exists according to the contract terms, revenue is recognized when the take-or-pay penalty is triggered.

(b) Marketing revenues

Marketing revenues principally represent the sales of oil and gas from the foreign partners under the production sharing contracts and revenues from the trading of oil and gas through the Company's subsidiaries. The cost of the oil and gas sold is included in "Crude oil and product purchases" in the consolidated statement of profit or loss and other comprehensive income. In addition, the Group's marketing activities in North America involves entering into contracts to purchase and sell crude oil, natural gas and other energy commodities, and use derivative contracts, including futures, forwards, swaps and options for hedging and trading purposes (collectively derivative contracts). Any change in the fair value is also included in marketing revenues.

(c) Other revenue

Other revenue mainly represents project management fees charged to foreign partners, handling fees charged to customers, the sales of diluents to third party and gains from disposal of oil and gas properties and is recognized when the services have been rendered or the properties have been disposed of. Reimbursement of insurance claims is recognized when the compensation becomes receivable.

(d) Dividend income

Dividend income is recognized when the Group's right to receive payment is established.

(e) Interest income

Interest income is recognized as it accrues using the effective interest method.

The Group presents taxes collected from customers in the consolidated statement of profit or loss and other comprehensive income on a net basis.

Share-based payment transactions

Employees (including directors) of the Group receive remuneration in the form of share-based payment transactions, whereby employees render services as consideration for equity instruments ("equity-settled transactions").

The cost of equity-settled transactions with employees is measured by reference to the fair value at the date at which they are granted. The fair value is determined by using the Black-Scholes option pricing model, further details of which are given in note 27.

The cost of equity-settled transactions is recognized, together with a corresponding increase in equity, over the period in which the performance and/or service conditions are fulfilled. The cumulative expense recognized for equity-settled transactions at the end of the each reporting period until the vesting date reflects the extent to which the vesting period has expired and the Group's best estimate of the number of equity instruments that will ultimately vest. The charge or credit to profit or loss for a period represents the movement in the cumulative expense recognized as at the beginning and end of that period.

No expense is recognized for awards that do not ultimately vest for the Group.

No equity-settled award was cancelled or modified during the years ended December 31, 2016, 2017 and 2018.

The dilutive effect of outstanding options is reflected as additional share dilution in the computation of earnings per share.

Retirement and termination benefits

The Group participates in defined contribution plans in accordance with local laws and regulations for full-time employees in the PRC and other countries in which it operates. The Group's contributions to these defined contribution plans are charged to profit or loss in the year to which they relate.

Borrowing costs

Borrowing costs consist of interest and other costs that an entity incurs in connection with the borrowing of funds. Borrowing costs directly relating to the acquisition, construction or production of a qualifying asset that necessarily takes a substantial period of time to get ready for its intended use or sale are capitalized as part of the cost of the respective assets. All other borrowing costs are expensed in the period in which they are incurred.

Foreign currencies

These consolidated financial statements are presented in RMB. Each entity in the Group maintains its books and records in its own functional currency. Foreign currency transactions recorded by the entities of the Group are initially recorded using their respective exchange rates ruling at the dates of the transactions. Monetary assets and liabilities denominated in foreign currencies are retranslated at the exchange rates ruling at the end of the reporting period. All differences arising on settlement or translation of monetary items are taken to profit or loss. Non-monetary items that are measured in terms of historical cost in a foreign currency are translated using the exchange rates at the dates of the initial transactions. Non-monetary items measured at fair value in a foreign currency are translated using the exchange rates at the date when the fair value was determined. The gain or loss arising on retranslation of a non-monetary item is treated consistently with the recognition of the gain or loss on change in fair value of the item.

The functional currencies of certain entities within the Group are currencies other than RMB. As at the end of the reporting period, the assets and liabilities of these entities are translated into the presentation currency of the Group at the exchange rates ruling at the reporting date, and their statement of profit or loss and other comprehensive income are translated into RMB at the weighted average exchange rates for the year. The resulting exchange differences are included in the cumulative translation reserve. On disposal of a foreign operation, the deferred cumulative amount recognized in equity relating to that particular foreign operation is recognized in profit or loss.

Operating leases

Leases where substantially all the rewards and risks of ownership of assets remain with the lessor are accounted for as operating leases. Where the Group is the lessee, rentals payable under operating leases are charged to profit or loss on the straight-line basis over the lease terms.

Prepaid land lease payments under operating leases in China are initially stated at cost and subsequently amortized on the straight-line basis over the lease terms.

Contingencies

A contingent liability is disclosed when the existence of an obligation will only be confirmed by future events or when the amount of the obligation cannot be measured reliably.

A contingent asset is not recognized in the financial statements, but is disclosed when an inflow of economic benefits is probable.

Significant accounting judgements, estimates and assumptions

The preparation of the consolidated financial statements in accordance with IFRSs and HKFRSs requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities at the date of the consolidated financial statements and the reported amounts of revenues and expenses during the reporting period. Estimates and judgements are continuously evaluated and are based on management's experience and other factors, including expectations of future events that are believed to be reasonable under the circumstances. However, actual outcomes can differ from these estimates.

In the process of applying the Group's accounting policies, the Directors have made the following judgements, estimates and assumptions, which have the most significant effect on the amounts recognized in the consolidated financial statements:

(a) Reserve base

Oil and gas properties are depreciated on a unit-of-production basis at a rate calculated by reference to proved reserves. Commercial reserves are determined using estimates of oil in place, recovery factors and future oil prices, the latter having an impact on the proportion of the gross reserves which are attributable to the host government under the terms of the production sharing contracts. The level of estimated commercial reserves is also a key determinant in assessing whether the carrying value of any of the Group's oil and gas properties has been impaired.

Pursuant to the oil and gas reserve estimation requirements under US Securities and Exchange Commission's rules, the Group uses the average, first-day-of-the-month oil price during the 12-month period before the ending date of the period covered by the consolidated financial statements to estimate its proved oil and gas reserves.

(b) Carrying value of oil and gas properties

The calculation of the unit-of-production rate for oil and gas properties amortization could be impacted to the extent that actual production in the future is different from current forecast production based on proved reserves. This would generally result from significant changes in any of the factors or assumptions used in estimating reserves. These factors could include changes in proved reserves, the effect on proved reserves of differences between actual oil and gas prices and oil and gas price assumptions and unforeseen operational issues.

(c) Recoverable amount of oil and gas properties

The Group makes an assessment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable, or when there is any indication that an impairment loss previously recognized for an asset in prior years may no longer exist or may have decreased. In any event, the Group would make an estimate of the asset's recoverable amount, which is calculated at the higher of the asset's value in use and its fair value less costs of disposal. The Group recognizes an impairment loss only if the carrying amount of an asset exceeds its recoverable amount. The Group charges an impairment loss to the profit or loss in the period in which it arises. A reversal of an impairment loss is credited to the profit or loss in the period in which it arises.

The calculations of the recoverable amount of assets require the use of estimates and assumptions. The key assumptions include, but are not limited to, future oil and gas prices, future production estimates, estimated future capital expenditures, estimated future operating expenses and the discount rate.

Changes in the key assumptions used, which could be significant, include updates to future pricing estimates, updates to future production estimates to align with the Group's anticipated drilling plan, changes in the Group's capital costs and operating expense assumptions, and discount rate. There is a significant degree of uncertainty with the assumptions used to estimate future cash flows due to various risk factors. The complex economic outlook may also materially and adversely affect the Group's key assumptions. Changes in economic conditions can also affect the discount rates applied in assessments of impairment.

Actual cash flows are likely to be different from those estimated or forecast since anticipated events frequently do not occur as expected and unforeseen events may arise. The Group's results of operations could be materially and adversely affected for the period in which future impairment charges are incurred.

The sensitivity analysis for the impairment testing involves estimates and judgments to consider numerous assumptions comprehensively. Those assumptions interact on each other and interrelate with each other complexly and do not have fixed patterns along with the changes in price. Accordingly, the Group believes that the preparation of the sensitivity analysis for the impairment testing will be impracticable. Changes in assumptions could affect impairment charges and reversals in the consolidated statement of profit or loss and other comprehensive income, and the carrying amounts of assets in the consolidated statement of financial position.

In the calculations of the recoverable amount of the oil and gas properties in a joint venture, the Group uses the approach above.

(d) Dismantlement costs

Dismantlement costs will be incurred by the Group at the end of the operating life of certain of the Group's facilities and properties. The ultimate dismantlement costs are uncertain and cost estimates can vary in response to many factors including changes to relevant legal requirements, the emergence of new restoration techniques or experience at other production sites. The expected timing and amount of expenditure can also change, for example, in response to changes in reserves or changes in laws and regulations or their interpretation. As a result, there could be significant adjustments to the provisions established which would affect future financial results.

(e) Taxes

Uncertainties exist with respect to the interpretation of complex tax regulations (including those applicable to tax credits) and the amount and timing of future taxable income. Given the wide range of international business relationships and the long term nature and complexity of existing contractual agreements, differences arising between the actual results and the assumptions made, or future changes to such assumptions, could necessitate future adjustments to tax income and expense already recorded. The Group establishes provisions, based on best estimates, for possible consequences of audits by the tax authorities of the respective countries in which it operates. The amount of such provisions is based on various factors, such as the Group's experience of previous tax audits and differing interpretations of tax regulations by the taxable entity and the responsible tax authority. Such differences of interpretation may arise on a wide variety of issues depending on the conditions prevailing in the respective group company's domicile.