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                                                                     EXHIBIT 5.1



                                 October 3, 2001



Equitable Resources, Inc.
One Oxford Centre, Suite 3300
301 Grant Street
Pittsburgh, PA 15219

Gentlemen:

         I am the Vice President, General Counsel and Secretary to Equitable
Resources, Inc., a Pennsylvania corporation (the "Company"), and I have acted in
such capacity in connection with the Registration Statement on Form S-8 being
filed with the Securities and Exchange Commission (the "Registration Statement")
for the purpose of registering under the Securities Act of 1933, as amended,
5,000,000 shares of Common Stock, no par value, which may be issued upon the
exercise of stock options and other stock awards under the 1999 Equitable
Resources, Inc. Long-Term Incentive Plan (the "Plan"). In such connection, I
have examined the originals, or copies thereof identified to my satisfaction, of
such corporate records of the Company and such other documents, records,
opinions and papers as I have deemed necessary or appropriate in order to give
the opinions hereinafter set forth.

         I understand that, prior to any sale or distribution of Common Stock
under the Plan the Registration Statement will have become effective under the
Securities Act of 1933 and the Pennsylvania Public Utility Commission shall have
issued an order approving the Company's issuance of Common Stock under the Plan.

         Based on the foregoing, I advise you that in my opinion:

         1. The Company has been duly organized and is a validly existing
corporation under the laws of the Commonwealth of Pennsylvania;

         2. The 5,000,000 shares of Common Stock which are being registered and
which have been authorized for issuance in accordance with the Plan, are, or
will be, when sold in accordance with the provisions of the Plan, legally
issued, fully paid and non-assessable.

         I hereby consent to the filing of my opinion as Exhibit 5.1 to the
Registration Statement.

                                      Very truly yours,

                                      /s/ Johanna G. O'Loughlin
                                      Johanna G. O'Loughlin
                                      Vice President, General Counsel
                                      and Secretary