2009 Press Releases

Onyx Pharmaceuticals Announces Concurrent Offerings of Four Million Shares of Common Stock and $200 Million Principal Amount of Convertible Senior Notes

Emeryville, CA. — Aug. 04, 2009

Onyx Pharmaceuticals, Inc. (Nasdaq: ONXX) today announced that it intends to offer, subject to market and other conditions, four million shares of its common stock and $200 million aggregate principal amount of its convertible senior notes due 2016 in concurrent underwritten public offerings. Onyx intends to grant the underwriters 30-day options to purchase up to an additional 600,000 shares of its common stock and up to an additional $30 million aggregate principal amount of its convertible senior notes in connection with the offerings. All of the shares of common stock and the notes are being offered by Onyx.

Prior to May 15, 2016, the notes will be convertible only upon specified events, and, thereafter until maturity, at any time. Upon conversion, the notes may be settled by the payment of cash, shares of Onyx common stock or a combination thereof, at the option of Onyx. Onyx will have the right to redeem the notes in whole or in part at a specified redemption price at any time on or after August 20, 2013. Final terms of the notes, including the interest rate, conversion price and other terms, will be determined at the time of pricing of the offering.

Goldman, Sachs & Co. is acting as the sole book-running manager for these offerings. The common stock offering and the convertible senior note offering are being conducted as separate public offerings by means of separate prospectus supplements, and neither of these offerings is contingent upon the consummation of the other.

These offerings are being made pursuant to an effective shelf registration statement previously filed with the U.S. Securities and Exchange Commission (the “SEC”). For each offering, a prospectus supplement and accompanying prospectus describing the terms of such offering will be filed with the SEC. Before investing in either offering, interested parties may read the prospectus supplement and the accompanying prospectus for such offering and the other documents Onyx has filed with the SEC. These documents are incorporated by reference in the prospectus supplement and the accompanying prospectus and provide more complete information about Onyx and the offering. Copies of the prospectus supplements, when available, may be obtained from Goldman, Sachs & Co., Prospectus Department, 85 Broad Street, New York, NY 10004, telephone: 1-866-471-2526, facsimile 212-902-9316 or by emailing prospectus-ny@ny.email.gs.com. Electronic copies of the prospectus supplements may be obtained by visiting EDGAR on the SEC website at www.sec.gov.

This communication shall not constitute an offer to sell or the solicitation of an offer to buy the securities described herein, nor shall there be any sale of these securities in any state in which such offer, solicitation or sale would be unlawful prior to registration or qualification under the securities laws of any such state or jurisdiction. The offerings of the securities may be made only by means of a prospectus supplement and accompanying prospectus.

About Onyx Pharmaceuticals, Inc.
Onyx Pharmaceuticals, Inc. is a biopharmaceutical company committed to improving the lives of people with cancer. The company, in collaboration with Bayer HealthCare Pharmaceuticals Inc., is developing and marketing Nexavar® (sorafenib) tablets, a small molecule drug.

This news release also contains “forward-looking statements” of Onyx within the meaning of the federal securities laws. These forward-looking statements include without limitation, statements regarding expectations as to completion, timing and size of any public offering. These statements are subject to risks and uncertainties that could cause actual results and events to differ materially from those anticipated, including risks and uncertainties related to the financial markets. Reference should be made to Onyx’s Annual Report on Form 10-K for the year ended December 31, 2008, filed with the SEC under the heading “Risk Factors” for a more detailed description of such factors, as well as Onyx’s subsequent Quarterly Reports on Form 10-Q. Readers are cautioned not to place undue reliance on these forward-looking statements that speak only as of the date of this release. Onyx undertakes no obligation to update publicly any forward-looking statements to reflect new information, events or circumstances after the date of this release except as required by law.