1 LAW OFFICES FENNEMORE CRAIG A PROFESSIONAL CORPORATION CALVIN H. UDALL JAMES POWERS JAMES M. BUSH ARTHUR D. EHRENREICH OFFICES IN PHOENIX AND TUCSON C. WEBB CROCKETT KENNETH J. SHERK NEAL KURN ROBERT P. ROBINSON MICHAEL PRESTON GREEN JOHN D. EVERROAD JAMES W. JOHNSON F. PENDLETON GAINES, III ROBERT J. HACKETT JAY S. RUFFNER JORDAN GREEN LOUIS F. COMUS, JR. 3003 NORTH CENTRAL AVENUE DONALD R. GILBERT RONALD L. BALLARD TIMOTHY J. BURKE RONALD J. STOLKIN SUITE 2600 STEPHEN M. SAVAGE ROGER T. HARGROVE WILLIAM L. KURTZ MARK A. NESVIG PHOENIX, ARIZONA 85012-2913 JAMES R. HUNTWORK DAVID T. MADDOX GEORGE T. COLE LAUREN J. CASTER Phone: (602) 916-5000 LELAND M. JONES TIMOTHY BERG C. OWEN PAEPKE WILLIAM L. THORPE Fax: (602) 916-5999 CHARLES M. KING DAVID T. COX CYNTHIA L. SHUPE MICHAEL V. MULCHAY PHILLIP F. FARGOTSTEIN PAUL J. MOONEY CATHY L. REECE DAVID A. WEATHERWAX WRITER'S DIRECT GRAEME HANCOCK RITA A. EISENFELD DAVID N. HEAP DON J. MINER Phone: (602) 916-5307 RAY K. HARRIS MARGARET R. GALLOGLY KAYE L. McCARTHY SCOTT M. FINICAL Fax: (602) 916-5507 DAVID E. VIEWEG ANDREW M. FEDERHAR GREGG HANKS KAREN CIUPAK McCONNELL kmcconne@fclaw.com JAY S. KRAMER CHRISTOPHER L. CALLAHAN REBECCA BURNHAM PIERONI JIM WRIGHT BRYAN A. ALBUE J. BARRY SHELLEY LESA J. STOREY CHRISTOPHER P. STARING JANET W. LORD ROBERT E. COLTIN JOHN RANDALL JEFFERIES ROBERT D. ANDERSON JOHN J. BALITIS, JR. JAMES J. TRIMBLE JANICE PROCTER-MURPHY ROBERT J. KRAMER JEAN M. SULLIVAN KEITH L. HENDRICKS KAREN A. CUROSH THERESA DWYER MARK H. BRAIN SCOTT H. THOMAS ELIZABETH M. BEHNKE W.T. EGGLESTON, JR. M. VIRGINIA PERRY ANNA P. WINSETT SUSAN GAYLORD WILLIS PAUL F. WILLE DOUGLAS C. NORTHUP MARC H. LAMBER RICHARD A. KASPER KENDIS K. MUSCHEID STEPHEN A. GOOD SUSAN M. CIUPAK JEFFREY S. PITCHER STACIE KEIM SMITH DEWAIN D. FOX JEFFREY S. SILVYN BRETT L. HOPPER VALERIE B. NOON AMY ABDO ANDERSON JAMES D. BURGESS SCOTT L. ALTES MARY BETH PHILLIPS ERIN E. FLAHARTY WILLIAM P. WICHTERMAN RUSSELL O. FARR THOMAS F. O'MALLEY, III JANNA B. DAY SUSAN M. HASSIG DAVID M. CALL VERA E. MUNOZ SAL J. RIVERA CAREY J. FOX JOEL B. SHAPIRO THEODORE D. SETZER MICHELLE G. MARSHALL STACEY A. KELLY JOSEPH SCIARROTTA, JR. JOHN D. BETHEA * Admitted to practice in New York STANLEY S. WEITHORN * ** Admitted to practice in Ohio, JOSEPH B. CONN ** Maryland and District of Columbia Senior Counsel EXHIBIT 5.1 May 18, 1998 Board of Directors Giant Industries, Inc. 23733 North Scottsdale Road Scottsdale, Arizona 85255 RE: Giant Industries, Inc. Registration Statement on Form S-4 for the Merger with Holly Corporation Ladies and Gentlemen: We have acted as special counsel to Giant Industries, Inc., a Delaware corporation (the "Company"), in connection with the Registration Statement on Form S-4, No. 333-51785 (the "Registration Statement"), filed by the Company with the Securities and Exchange Commission (the "Commission"). The Registration Statement relates to the registration under the Securities Act of 1933, as amended (the "Act"), of 11,050,000 shares (the "Merger Shares") of the Company's Common Stock, par value $.01 per share, to be issued pursuant to the Merger Agreement (as defined below) between the Company and Holly Corporation ("Holly"). In connection with this opinion, we have examined originals or copies, certified or otherwise identified to our satisfaction, of (i) the Agreement and Plan of Merger between the Company and Holly, dated April 14, 1998 (the "Merger Agreement"), (ii) the existing Certificate of Incorporation and Bylaws of the Company, (iii) the proposed Restated Certificate of Incorporation and the proposed Amended and Restated Bylaws of the Company, (iv) certain resolutions of the Board of Directors of the Company relating to the Merger Agreement, the Restated Certificate of Incorporation and the Amended and Restated Bylaws of the Company, (v) the Registration Statement filed with the Commission, and (vi) such other corporate records, agreements, documents and other instruments of the Company and such certificates or comparable documents of public officials and of officers and representatives of the Company as we deemed necessary or appropriate for purposes of rendering the opinions set forth below. 2 FENNEMORE CRAIG Giant Industries, Inc. May 18, 1998 Page 2 In such examination and in rendering the opinions set forth below, we have assumed (i) the legal capacity of all natural persons, (ii) the genuineness of all signatures, (iii) the authority of all signatories, (iv) the authenticity and completeness of all documents submitted to us as forms of the documents to be executed, (v) the conformity to original documents of all documents submitted to us as certified or photostatic copies, and (vi) that the Merger Shares will be issued as described in the Merger Agreement and the Registration Statement. As to any facts material to this opinion which we did not independently establish or verify, we have relied upon statements or representations of officers and/or other representatives of the Company and others, all of which statements and representations we have assumed to be true and correct in all respects as of the date hereof. Based upon and subject to the foregoing, and to the assumptions, limitations, qualifications and exceptions set forth herein, it is our opinion that the Merger Shares have been duly authorized and, after the Registration Statement becomes effective and when the Merger Shares are issued to Holly in accordance with the Merger Agreement, the Merger Shares will be duly issued, fully paid and nonassessable. We are qualified to practice law in the State of Arizona. We express no opinion as to, and for the purposes of the opinions set forth herein, we have conducted no investigation of, and do not purport to be experts on, any laws other than the laws of the State of Arizona and the General Corporation Law of the State of Delaware. This opinion is rendered as of the date hereof, and we undertake no obligation to update this opinion should it no longer remain accurate by change in factual circumstances, law, judicial decision or otherwise. This opinion is furnished only to, and is solely for the benefit of, the addressee named above and, except with our prior written consent, is not to be used, circulated, quoted or otherwise referred to or disseminated for any other purpose or relied upon by any person or entity. Notwithstanding the foregoing, we hereby consent to the filing of this opinion with the Commission as Exhibit 5.1 to the Registration Statement and to the reference to this firm under the heading "LEGAL MATTERS" in the Joint Proxy Statement/Prospectus forming a part of the Registration Statement. In giving this consent, we do not thereby admit that we are included in the category of persons whose consent is required under Section 7 of the Act or the rules and regulations of the Commission. 3 FENNEMORE CRAIG Giant Industries, Inc. May 18, 1998 Page 3 Very truly yours, /s/ Fennemore Craig, a Professional Corporation Fennemore Craig, a Professional Corporation