June 20, 2011 – Frontier Oil Corporation (NYSE: FTO) (“Frontier”) today announced that it has submitted written notice to the New York Stock Exchange (the “NYSE”) of its intention to voluntarily delist its common stock, no par value, from the NYSE pending successful closing of the merger of Frontier with Holly Corporation (the “Closing”). Pending the Closing, Frontier intends to have the NYSE file a Form 25 with the Securities and Exchange Commission (the “SEC”) on July 1, 2011 to delist its common stock. Also pending the Closing, Frontier intends to file a Form 15 with the SEC on or about July 11, 2011 in order to terminate the registration of the common stock under Section 12 of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), and to notify the SEC of the automatic suspension of its public reporting obligations under Sections 13(a) and 15(d) of the Exchange Act. As previously announced, Frontier entered into an Agreement and Plan of Merger, dated as of February 21, 2011 (the “Merger Agreement”), by and among Frontier, Holly Corporation (“Holly”), and North Acquisition, Inc. (“Merger Sub”) pursuant to which Merger Sub will merge with and into Frontier (the “Merger”). Pursuant to the Merger Agreement, upon consummation of the Merger (a) each outstanding share of Frontier common stock (subject to certain exceptions) will be converted into 0.4811 shares of Holly common stock, (b) certain outstanding Frontier equity awards issued under the Frontier Omnibus Incentive Compensation Plan (as amended and as may be further amended from time to time, the “Frontier Plan”) will vest and be converted into shares of Holly common stock and (c) certain outstanding Frontier equity awards issued under the Frontier Plan will be converted into comparable Holly equity awards. As a result of the Merger, a trading market for Frontier’s common stock will no longer exist. In addition, upon the delisting, Frontier will qualify to terminate the registration of its common stock under Section 12 of the Exchange Act and exit the SEC periodic reporting system. The common stock will not be listed or registered on another national securities exchange or for quotation in a quotation medium.