Basis of Presentation

3 Months Ended

Mar. 31, 2013

Basis of Presentation

Basis of Presentation

Note 1. Basis of Presentation

The accompanying unaudited Condensed Consolidated Financial Statements have been prepared in accordance with U.S. generally accepted accounting principles (“GAAP”) for interim financial information and with the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, they do not include all of the information and footnotes required by GAAP for complete financial statements. The unaudited financial statements furnished herein include all adjustments necessary for a fair presentation of Onyx Pharmaceuticals, Inc.’s (“Onyx” or the “Company”) financial position at March 31, 2013, and the results of its operations and cash flows for the three months ended March 31, 2013 and 2012. These interim financial statements have been prepared on a basis consistent with the Company’s annual financial statements. The Condensed Consolidated Balance Sheet at December 31, 2012 has been derived from the audited financial statements at that date, but does not include all of the information and footnotes required by GAAP for complete financial statements. This Form 10-Q should be read in conjunction with the Consolidated Financial Statements and accompanying Notes contained in the Company’s Annual Report on Form 10-K for the year ended December 31, 2012.

Significant Accounting Policies

As of March 31, 2013, there have been no material changes to the Company’s significant accounting policies as compared to the significant accounting policies described in the Company’s Annual Report on Form 10-K for the year ended December 31, 2012.

Use of Estimates and Assumptions

The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. Thus, actual results could differ from those estimates. In the opinion of management, all adjustments consisting of normal recurring accruals considered necessary for a fair presentation have been included. Operating results for the three months ended March 31, 2013 are not necessarily indicative of the results that may be expected for the year ending December 31, 2013 or for any other future operating periods.

Principles of Consolidation

The unaudited Condensed Consolidated Financial Statements include the accounts of the Company and its wholly owned subsidiaries. All significant intercompany balances and transactions have been eliminated in consolidation.

Segment Reporting

The Company operates in one segment — the discovery and development of novel cancer therapies.

Concentration of Credit Risk

Financial instruments which potentially subject the Company to concentrations of credit risk consist of accounts receivable.

Recent Accounting Pronouncements

In February 2013, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) No. 2013-02, “Reporting of Amounts Reclassified Out of Accumulated Other Comprehensive Income.” Under this standard, entities will be required to disclose additional information with respect to changes in accumulated other comprehensive income (AOCI) balances by component and significant items reclassified out of AOCI. Expanded disclosures for presentation of changes in AOCI involve disaggregating the total change of each component of other comprehensive income (for example, unrealized gains or losses on available for sale marketable securities) as well as presenting separately for each such component the portion of the change in AOCI related to (1) amounts reclassified into income and (2) current-period other comprehensive income. Additionally, for amounts reclassified into income, disclosure in one location would be required, based upon each specific AOCI component, of the amounts impacting individual income statement line items. Disclosure of the income statement line item impacts will be required only for components of AOCI reclassified into income in their entirety. Therefore, disclosure of the income statement line items affected by AOCI components such as net periodic benefit costs would not be included. The disclosures required with respect to income statement line item impacts would be made in either the notes to the consolidated financial statements or parenthetically on the face of the financial statements. This ASU is effective beginning January 1, 2013. Because this standard only impacts presentation and disclosure requirements, its adoption did not have a material impact on the Company’s consolidated results of operations or financial condition.