Our reportable segments are based upon our internal organizational structure; the manner in which our operations are managed; the criteria used by our Chief Executive Officer, who is our Chief Operating Decision Maker ("CODM"), to evaluate segment performance; the availability of separate financial information; and overall materiality considerations. Effective the first quarter of 2018, our business has three reportable segments: (i) Travel Network, (ii) Airline Solutions and (iii) Hospitality Solutions. In conjunction with this change, we have modified the methodology we have historically used to allocate shared corporate technology costs. Each segment now reflects a portion of our shared corporate costs that historically were not allocated to a business unit, based on relative consumption of shared technology infrastructure costs and defined revenue metrics. These changes have no impact on our consolidated results of operations, but result in a decrease of individual segment profitability only.

Our CODM utilizes Adjusted Gross Profit, Adjusted Operating Income and Adjusted EBITDA as the measures of profitability to evaluate performance of our segments and allocate resources. Corporate includes a technology organization that provides development and support activities to our segments. The majority of costs associated with our technology organization are allocated to the segments primarily based on the segments' usage of resources. Benefit expenses, facility costs and depreciation expense on the corporate headquarters building are allocated to the segments based on headcount. Unallocated corporate costs include certain shared expenses such as accounting, finance, human resources, legal, corporate systems, amortization of acquired intangible assets, impairment and related charges, stock-based compensation, restructuring charges, legal reserves and other items not identifiable with one of our segments.

The performance of our segments is evaluated primarily on Adjusted Gross Profit, Adjusted Operating Income and Adjusted EBITDA which are not recognized terms under GAAP. Our uses of Adjusted Gross Profit, Adjusted Operating Income and Adjusted EBITDA have limitations as analytical tools, and should not be considered in isolation or as a substitute for analysis of our results as reported under GAAP.

We define Adjusted Gross Profit as operating income adjusted for selling, general and administrative expenses, impairment and related charges, the cost of revenue portion of depreciation and amortization, restructuring and other costs, amortization of upfront incentive compensation, and stock-based compensation included in cost of revenue.

We define Adjusted EBITDA as income from continuing operations adjusted for impairment and related charges, depreciation and amortization of property and equipment, amortization of capitalized implementation costs, acquisition-related amortization, amortization of upfront incentive consideration, interest expense, net, loss on extinguishment of debt, other, net, restructuring and other costs, acquisition-related costs, litigation costs, net, stock-based compensation and provision for income taxes.


	Year Ended December 31,
	2019		2018		2017
Revenue
Travel Network	$	2,882,662	$	2,806,194	$	2,550,470
Airline Solutions	840,338		822,747		816,008
Hospitality Solutions	292,880		273,079		258,352
Eliminations	(40,892)		(35,064)		(26,346)
Total revenue	$	3,974,988	$	3,866,956	$	3,598,484
Adjusted Gross Profit (Loss)^(a)
Travel Network	$	1,016,695	$	1,098,052	$	1,071,249
Airline Solutions	326,610		355,079		366,255
Hospitality Solutions	64,842		83,333		88,477
Corporate	(16,341)		(15,056)		(25,795)
Total	$	1,391,806	$	1,521,408	$	1,500,186
Adjusted Operating Income (Loss) ^(b)
Travel Network	$	648,838	$	755,811	$	746,625
Airline Solutions	80,428		111,146		137,932
Hospitality Solutions	(21,632)		12,881		9,670
Corporate	(194,226)		(178,406)		(188,078)
Total	$	513,408	$	701,432	$	706,149
Adjusted EBITDA^(c)
Travel Network	$	852,856	$	951,709	$	923,615
Airline Solutions	251,442		293,577		296,437
Hospitality Solutions	31,466		52,824		42,784
Total segments	1,135,764		1,298,110		1,262,836
Corporate	(189,404)		(173,720)		(184,265)
Total	$	946,360	$	1,124,390	$	1,078,571
Depreciation and amortization
Travel Network	$	121,083	$	118,276	$	109,579
Airline Solutions	171,014		182,431		158,505
Hospitality Solutions	53,098		39,943		33,114
Total segments	345,195		340,650		301,198
Corporate	69,426		72,694		99,673
Total	$	414,621	$	413,344	$	400,871
Capital Expenditures
Travel Network	$	15,580	$	64,943	$	90,881
Airline Solutions	37,062		98,374		116,948
Hospitality Solutions	11,324		39,160		43,443
Total segments	63,966		202,477		251,272
Corporate	51,200		81,463		65,165
Total	$	115,166	$	283,940	$	316,437


	Year Ended December 31,
	2019		2018		2017
Adjusted Gross Profit	$	1,391,806	$	1,521,408	$	1,500,186
Less adjustments:
Selling, general and administrative	576,568		513,526		510,075
Impairment and related charges⁽⁷⁾	—		—		81,112
Cost of revenue adjustments:
Depreciation and amortization⁽¹⁾	340,889		341,653		317,812
Amortization of upfront incentive consideration⁽²⁾	82,935		77,622		67,411
Restructuring and other costs⁽⁴⁾	—		—		12,604
Stock-based compensation	27,997		26,591		17,732
Operating income	$	363,417	$	562,016	$	493,440


	Year Ended December 31,
	2019		2018		2017
Adjusted Operating income	$	513,408	$	701,432	$	706,149
Less adjustments:
Joint venture equity income	2,044		2,556		2,580
Impairment and related charges⁽⁷⁾	—		—		81,112
Acquisition-related amortization^(1c)	64,604		68,008		95,860
Restructuring and other costs⁽⁴⁾	—		—		23,975
Acquisition-related costs⁽⁵⁾	41,037		3,266		—
Litigation costs, net⁽⁶⁾	(24,579)		8,323		(35,507)
Stock-based compensation	66,885		57,263		44,689
Operating income	$	363,417	$	562,016	$	493,440


	Year Ended December 31,
	2019		2018		2017
Adjusted EBITDA	$	946,360	$	1,124,390	$	1,078,571
Less adjustments:
Impairment and related charges⁽⁷⁾	—		—		81,112
Depreciation and amortization of property and equipment^(1a)	310,573		303,612		264,880
Amortization of capitalized implementation costs^(1b)	39,444		41,724		40,131
Acquisition-related amortization^(1c)	64,604		68,008		95,860
Amortization of upfront incentive consideration⁽²⁾	82,935		77,622		67,411
Interest expense, net	156,391		157,017		153,925
Loss on extinguishment of debt	—		633		1,012
Other, net⁽³⁾	9,432		8,509		(36,530)
Restructuring and other costs⁽⁴⁾	—		—		23,975
Acquisition-related costs⁽⁵⁾	41,037		3,266		—
Litigation costs, net⁽⁶⁾	(24,579)		8,323		(35,507)
Stock-based compensation	66,885		57,263		44,689

Provision for income taxes⁽⁸⁾	35,326		57,492		128,037
Income from continuing operations	$	164,312	$	340,921	$	249,576

(2)Our Travel Network business at times provides upfront incentive consideration to travel agency subscribers at the inception or modification of a service contract, which are capitalized and amortized to cost of revenue over an average expected life of the service contract, generally over three to ten years. This consideration is made with the objective of increasing the number of clients or to ensure or improve customer loyalty. These service contract terms are established such that the supplier and other fees generated over the life of the contract will exceed the cost of the incentive consideration provided up front. These service contracts with travel agency subscribers require that the customer commit to achieving certain economic objectives and generally have terms requiring repayment of the upfront incentive consideration if those objectives are not met.

(3)In 2019, Other, net primarily includes foreign exchange gains and losses related to the remeasurement of foreign currency denominated balances included in our consolidated balance sheets into the relevant functional currency. In 2018, we recognized an expense of $5 million related to our liability under the TRA offset by a gain of $8 million on the sale of an investment. In 2017, we recognized a benefit of $60 million due to a reduction to our liability under the TRA primarily due to a provisional adjustment resulting from the enactment of TCJA which reduced the U.S. corporate income tax rate (see Note 7. Income Taxes), offset by a loss of $15 million related to debt modification costs associated with a debt refinancing. In addition, all periods presented include foreign exchange gains and losses related to the remeasurement of foreign currency denominated balances included in our consolidated balance sheets into the relevant functional currency.

(4)Restructuring and other costs represents charges associated with business restructuring and associated changes implemented which resulted in severance benefits related to employee terminations, integration and facility opening or closing costs and other business reorganization costs. We recorded $25 million in charges associated with an announced action to reduce our workforce in 2017. These reductions aligned our operations with business needs and implemented an ongoing cost and organizational structure consistent with our expected growth needs and opportunities.

(6)Litigation costs, net represent charges associated with antitrust and other foreign non-income tax contingency matters. In 2019, we recognized the reversal of our previously accrued loss related to US Airways legal matter for $32 million. In 2018, we recorded non-income tax expense of $5 million for tax, penalties and interest associated with certain non-income tax claims for historical periods regarding permanent establishment in a foreign jurisdiction. In 2017, we recorded a $43 million reimbursement, net of accrued legal and related expenses, from a settlement with our insurance carriers with respect to the American Airlines litigation. See Note 16. Commitments and Contingencies.

(7)Impairment and related charges represents an $81 million impairment charge recorded in 2017 associated with net capitalized contract costs related to an Airline Solutions' customer based on our analysis of the recoverability of such amounts. See Note 4. Impairment and Related Charges for additional information.

(8)In 2018, the provision for income taxes includes a benefit of $27 million related to the enactment of the TCJA for deferred taxes and foreign tax effects. In 2017, provision for income taxes includes a provisional impact of $47 million recognized as a result of the enactment of the TCJA in December 2017. See Note 7. Income Taxes.

A significant portion of our revenue is generated through transaction-based fees that we charge to our customers. For Travel Network, this fee is in the form of a transaction fee for bookings on our GDS; for Airline Solutions and Hospitality Solutions, this fee is a recurring usage-based fee for the use of our SaaS and hosted systems, as well as implementation fees and professional service fees. Transaction-based revenue accounted for approximately 94%, 95% and 95% of our Travel Network revenue for each of the years ended December 31, 2019, 2018 and 2017. Transaction-based revenue accounted for approximately 80%, 81% and 74% for the years ended December 31, 2019, 2018 and 2017, respectively, of our Airline Solutions revenue. Transaction-based revenue accounted for approximately 80%, 81% and 83% for the years ended December 31, 2019, 2018 and 2017, respectively, of our Hospitality Solutions revenue. All joint venture equity income relates to Travel Network.

Our revenues and long-lived assets, excluding goodwill and intangible assets, by geographic region are summarized below. Revenue of our Travel Network business is attributed to countries based on the location of the travel supplier. For Airline Solutions and Hospitality Solutions, revenue is attributed to countries based on the location of the customer. The majority of our revenues and long-lived assets are derived from the United States, Europe, and Asia-Pacific ("APAC") as follows (in thousands):