<PAGE>

                                                                     Exhibit 5.1

                                                             March 29, 2002


                               [Baker Botts Logo]

00D805.0321

Pennzoil-Quaker State Company
Pennzoil Place
700 Milam Street
Houston, Texas 77002

                         Pennzoil-Quaker State Company
                           10% Senior Notes Due 2008

Ladies and Gentlemen:

   As set forth in the Registration Statement on Form S-4 (File No. 333-84640)
(the "Registration Statement") filed by Pennzoil-Quaker State Company, a
Delaware corporation (the "Company") and the subsidiaries of the Company named
in Schedule I hereto (the "Guarantors") with the Securities and Exchange
Commission (the "Commission") under the Securities Act of 1933, as amended (the
"Securities Act"), relating to the issuance by the Company of $250,000,000
aggregate principal amount of 10% Senior Notes Due 2008 (the "New Notes") and
the issuance by the Guarantors of guarantees (the "Guarantees") with respect to
the New Notes, we are passing upon certain legal matters in connection with the
New Notes of the Company and the Guarantees of the Guarantors. The New Notes
and the Guarantees are to be offered by the Company and the Guarantors,
respectively, in exchange (the "Exchange Offer") for a like aggregate principal
amount of the Company's issued and outstanding 10% Senior Notes Due 2008 (the
"Old Notes") and related guarantees. The New Notes and the Guarantees will be
issued under an Indenture dated as of November 2, 2001 (the "Indenture") among
the Company, the Guarantors and JPMorgan Chase Bank (formerly known as The
Chase Manhattan Bank), as trustee. At your request, this opinion is being
furnished to you for filing as Exhibit 5.1 to the Registration Statement.


   In our capacity as counsel to the Company and the Guarantors in the
connection referred to above, we have examined the Registration Statement, the
Indenture (including each guarantee set forth therein) and the form of the New
Notes, each of which will be filed with the Commission as an exhibit to the
Registration Statement. We have also examined originals, or copies certified or
otherwise identified, of (i) the Company's Restated Certificate of
Incorporation and Bylaws, each as amended to date, (ii) corporate records of
the Company, including minute books of the Company as furnished to us by the
Company, (iii) the charter, bylaws or other governing documents of each of the
Guarantors, (iv) corporate or partnership records of each of the Guarantors,
including minute books of each of the Guarantors furnished to us by the
Guarantors, (v) certificates of public officials and of representatives of the
Company and the Guarantors, and (vi) statutes and other instruments and
documents as a basis for the opinions hereinafter expressed. In giving the
opinions set forth below, we have relied upon certificates of officers or other
representatives of the Company and the Guarantors with respect to the accuracy
of the factual matters contained in such certificates. In making our
examination, we have assumed that all signatures on documents examined by us
are genuine, all documents submitted to us as originals are authentic and
complete and all documents submitted to us as certified or photostatic copies
conform to the originals thereof.
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   On the basis of the foregoing, and subject to the assumptions, limitations
and qualifications set forth herein, we are of the opinion that when (i) the
Registration Statement has become effective under the Securities Act and the
Indenture has been qualified under the Trust Indenture Act of 1939, as amended,
and (ii) the New Notes have been duly executed, authenticated, issued and
delivered in accordance with the provisions of the Indenture and the terms of
the Exchange Offer as contemplated in the Registration Statement, the New Notes
and the Guarantees will constitute legal, valid and binding obligations of the
Company and the Guarantors, respectively, enforceable against them in
accordance with their terms.

   Our opinion set forth above is subject to the effects of (i) bankruptcy,
insolvency, fraudulent conveyance, reorganization, moratorium and other similar
laws relating to or affecting creditors' rights generally, (ii) general
principles of equity and public policy (regardless of whether considered in a
proceeding in equity or at law) and (iii) an implied covenant of good faith and
fair dealing. Furthermore, the opinion set forth above is limited in all
respects to matters of the laws of the States of Maryland, Texas and New York,
the General Corporation Law of the State of Delaware and the applicable federal
laws of the United States, each as in effect on the date hereof. In rendering
the opinion set forth above with respect to the laws of the State of Maryland,
we have relied, with your consent, in all respects as to matters regarding the
laws of the State of Maryland on the opinion of counsel in such State that has
been furnished to you.

   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 our Firm
under the heading "Legal Matters" in the prospectus forming a part of the
Registration Statement. In giving this consent, we do not hereby admit that we
are in the category of persons whose consent is required under Section 7 of the
Securities Act or the rules and regulations of the Commission thereunder.

                                          Very truly yours,

                                          /s/ BAKER BOTTS L.L.P.
                                          -------------------------------------
                                          Baker Botts L.L.P.

DWT/STW/HK
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                                   Schedule I

                                   Guarantors

<TABLE>
<CAPTION>
                                                       State or Other
                                                       Jurisdiction of
                                                        Incorporation
      Guarantor                                        or Organization
      ---------                                        ---------------
      <S>                                              <C>
      Blue Coral, Inc.                                    Delaware
      Jiffy Lube International, Inc.                      Delaware
      Jiffy Lube International of Maryland, Inc.          Maryland
      Medo Industries, Inc.                               New York
      Pennzoil-Quaker State Canada Holding Company        Delaware
      Pennzoil-Quaker State International Corporation     Delaware
      Q Lube, Inc.                                        Delaware
</TABLE>