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                                                                    EXHIBIT 99.7





                             SHAREHOLDERS AGREEMENT

             SHAREHOLDERS AGREEMENT (this "Shareholders Agreement") dated as of
July 17, 1998, by and among M & M NOMINEE L.L.C., a Delaware limited liability
company ("Purchaser"), Rafael Vaquero Bazan and Fernando Camacho Casas
(collectively, the "Executives"). Certain terms used herein are defined in
Section 10.

                               W I T N E S S E T H

             WHEREAS, contemporaneously herewith and conditioned hereon,
Purchaser and The UniMark Group, Inc. (the "Company") are entering into a
Purchase Agreement (the "Purchase Agreement") providing for the issuance by the
Company and the purchase by Purchaser of shares of common stock, par value $0.01
per share, of the Company (the "Common Stock"); and

             WHEREAS, the Executives and Purchaser desire to provide for certain
rights and restrictions with regard to their respective ownership of Common
Stock.

             NOW, THEREFORE, in consideration of the mutual covenants herein
contained, the parties agree as follows:

1.       Restriction of Sale. (a) From the date hereof until the 18 month 
anniversary hereof, the Executives shall not sell, transfer, assign, exchange,
pledge, encumber or otherwise dispose of (each, a "Transfer") any shares of
Common Stock that they now own or hereafter acquire or grant any option or right
to purchase such shares or any legal or beneficial interest therein, except in
accordance with the provisions of this Shareholders Agreement. Notwithstanding
the foregoing, nothing herein shall prevent either Executive from effecting a
transfer of Common Stock if he is required to do so pursuant to either the
Margin Agreement between Rafael Vaquero Bazan and Everen Securities, Inc. or the
Margin Agreement between Fernando Camacho Casas and First London Securities
Corporation.

         (b)      Notwithstanding the provisions of Section 1(a), the Executives
may Transfer shares of Common Stock as follows:

                  (i)    each Executive may sell up to 25% of his shares of 
         Common Stock in a broadly distributed bona fide public offering of
         Common Stock pursuant to the Securities Act of 1933, as amended or in
         regular broker transactions pursuant to Rule 144A promulgated
         thereunder;
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                  (ii)   each Executive may Transfer his shares of Common Stock
         with the prior written consent of Purchaser; and

                  (iii)  each Executive may Transfer his shares to a member of
         his immediate family;

provided, however, that in the case of clauses (ii) and (iii) the transferee in
such Transfer agrees in writing to be bound by all the terms of this
Shareholders Agreement (such transferee being herein referred to as the
"Permitted Transferee") applicable to the Executive as if the Permitted
Transferee originally had been a party hereto.

         (c)      From the date hereof until the first anniversary of the date
hereof, Purchaser may not Transfer any shares of Common Stock except to an
Affiliate of Purchaser who agrees to be bound by the provisions hereof as if
such Affiliate transferee were originally a party hereto. At any time before, on
or after the first anniversary hereof, Purchaser shall not transfer any shares
of Common Stock to an Affiliate without causing such Affiliate to agree in
writing to be bound by the provisions hereof as if such Affiliate were
originally a party hereto.

2.       Buy - Sell Arrangement. (a) At any time after the first anniversary of
the date hereof, but only for so long as both a Governance Termination Event and
a Principal Termination Event have not occurred, if either group believes, in
its good faith judgment that a bona fide dispute exists between the Groups, then
such Group (the "Initiating Group"), by written notice (the "Notice") to the
other Group (the "Other Group"), may initiate a buy-sell option (the "Option")
subject to the terms and conditions set forth below.

         (b)      The Initiating Group may initiate the Option only if the
holders of at least 75% of its Specified Shares approve such initiation. All
other actions taken with respect to the Option by a Group shall require the
approval of the holders of at least a majority of its Specified Shares.

         (c)      The Notice shall specify a price per share (or other security)
for all of the Specified Shares owned by the Other Group. The Other Group shall
have the irrevocable Option to elect either (i) to sell (the "Sale Option") to
the Initiating Group (or its designee) all of the Specified Shares owned by the
Other Group at the date of receipt of the Notice (the "Receipt Date") at the
price per share (or other security) set forth in the Notice or (ii) to purchase
(the "Purchase Option") all of the Specified Shares owned by the Initiating
Group on the Receipt Date at the price per share (or other security) set forth
in the Notice. Such election, which shall be irrevocable, shall be


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made by written notice from the Other Group to the Initiating Group within 15
days of the Receipt Date, provided however if the Other Group fails to duly make
an election in this time period, it shall conclusively be deemed to have elected
the Sale Option.

         (d)      The closing (the "Closing") of the purchase and sale under the
Sale Option or the Purchase Option shall take place at the offices of the
Company on a date specified in writing on at least 5 business days' notice by
the Group purchasing the Specified Shares (the "Buying Group") to the Group
selling its Specified Shares (the "Selling Group"), but in any event within 45
days of the Receipt Date (subject to adjournment if and to the extent necessary
to obtain any necessary governmental approvals or to satisfy any legal waiting
periods). The purchase price shall be payable by the Buying Group (or its
designee) to the Selling Group in U.S. dollars in cash or immediately available
funds at the Closing. At the Closing, the Selling Group shall transfer its
Specified Shares to the Buying Group (or its designee) and shall deliver such
Specified Shares to the Buying Group (or its designee), with appropriate
instruments of transfer, free and clear of any lien, claim or encumbrance.
Pending the Closing, the Specified Shares of the Selling Group shall be voted by
the Buying Group, and appropriate proxies shall be promptly delivered to
effectuate this agreement.

         (e)      Each Group shall execute and deliver such instruments and
agreements, and shall take such actions, as may be reasonably requested by the
other Group to carry out the purposes of this Section 2.

3.       Agreement Not to Compete. (a) Each of the Executives agrees that for so
long as he is employed by, or a director of, the Company or a subsidiary of the
Company, and for 18 months thereafter, he will not (i) engage in any
"Competitive Activity," as defined below, within the world (including, without
limitation, anywhere in the United States of America) or (ii) directly or
indirectly solicit for employment, including, without limitation, recommending
to any subsequent employer the solicitation for employment of, any employee of
the Company.

         (b)      Each of the Executives represents and agrees that he has not
and, for so long as he is employed by or a director of the Company or a
subsidiary of the Company, and for three years thereafter, he will not,
appropriate for his own use, disclose to any third party, or authorize anyone
else to disclose, unless authorized by the Company, any secret, confidential,
proprietary or financial information concerning the operations, future plans,
methods of doing business, or financial condition of the Company or any
subsidiary or Affiliate thereof, or any customer lists, customer files or other
information relating to the customers of the Company, or any Subsidiary or
affiliate thereof that he obtained as a result of which his employment with the
Company and which is not 


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otherwise publicly available (unless it became publicly available in violation
of this Section 3(c)).

         (c)      Should a court of competent jurisdiction determine that any
provision of this Section 3 is unenforceable, in period of time, geographical
area, or otherwise, the parties hereto agree that the provision shall be
interpreted and enforced to the maximum extent which such court deems
enforceable.


4.       Severability. Any term, provision, covenant or restriction contained in
this Shareholders Agreement held by a court or other governmental authority of
competent jurisdiction to be invalid, void or unenforceable shall be ineffective
to the extent of such invalidity, voidness or unenforceability, but neither the
remaining terms, provisions, covenants or restrictions contained in this
Shareholders Agreement nor the validity or enforceability thereof in any other
jurisdiction shall be affected or impaired thereby. Any term, provision,
covenant or restriction contained in this Shareholders Agreement that is so
found to be so broad as to be unenforceable shall be interpreted to be as broad
as is enforceable.

5.       Successors; No Third Party Beneficiaries. The terms and conditions of
this Shareholders Agreement shall inure to the benefit of and be binding upon
the parties hereto and their respective successors and assigns. Nothing in this
Shareholders Agreement, expressed or implied, is intended to confer upon any
party, other than the parties hereto, and their respective successors and
assigns, any rights, remedies, obligations, or liabilities under or by reason of
this Shareholders Agreement, except as expressly provided herein.

6.       Notices. All notices or other communications which are required or
permitted hereunder shall be in writing and delivered personally, or sent by
telecopier or reputable overnight courier and delivered to the applicable
address as follows:

                  If to Rafael Vaquero Bazan, to him at:

                  Industrias Citricolas de Montemorelos, S.A. de C.V.
                  Carretera General Teran Kilometro 1
                  Apartado 87
                  Montemorelos, N.L., Mexico C.P 67500
                  Telecopier: (826) 3-44-17



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                  with a copy to:

                  Jakes Jordaan, Esq.
                  Jordaan & Pennington
                  300 Crescent Court, Suite 1605
                  Dallas, TX 75201
                  Telecopier: (214) 871-6560

                  If to Fernando Camacho Casas, to him at:

                  Operadora Agros, S.A. de C.V.
                  Rio Neva 17
                  Col. Cuauthemoc
                  06500 - Mexico, D.F.
                  Telecopier: 566-7026

                  with a copy to:

                  Jakes Jordaan, Esq.
                  Jordaan & Pennington
                  300 Crescent Court, Suite 1605
                  Dallas, TX 75201
                  Telecopier: (214) 871-6560

                  If to Purchaser, to:

                  M & M Nominee L.L.C.
                  c/o Soros Fund Managment
                  888 Seventh Avenue
                  New York, NY  10106
                  Attention: Chief Financial Officer
                  Telecopier: (212) 974-8399

                  with a copy to:

                  Promecap, S.C.
                  Bosque de Alisos No. 47A, 3er piso
                  Colonia Bosques de las Lomas
                  C.P. 05120 Mexico, D.F.
                  Mexico
                  Attention: Federico Chavez Peon
                  Telecopier: 011-525-259-6269


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                  with a copy to:

                  Joseph Stern, Esq.
                  Fried, Frank, Harris, Shriver & Jacobson
                  One New York Plaza
                  New York, New York  10004
                  Telecopier: (214) 859-4000


7.       Specific Performance. The parties hereto agree that if for any reason
Purchaser or the Company shall have failed to perform its obligations under this
Shareholders Agreement, then either party hereto seeking to enforce this
Shareholders Agreement against such non-performing party shall be entitled to
specific performance and injunctive and other equitable relief, and the parties
hereto further agree to waive any requirement for the securing or posting of any
bond in connection with the obtaining of any such injunctive or other equitable
relief. This provision is without prejudice to any other rights that either
party hereto may have against the other party hereto for any failure to perform
its obligations under this Shareholders Agreement.

8.       Governing Law. This Shareholders Agreement shall be governed by the
laws of the State of Delaware, without giving effect to the conflict of laws
principles thereof. Each party hereby irrevocably and unconditionally consents
to submit to the exclusive jurisdiction of the courts of the State of Delaware
and of the United States of America located in Wilmington, Delaware, for any
Litigation (and agrees not to commence any Litigation except in any such court).
Each party hereby irrevocably and unconditionally waives any objection to the
laying of venue of any Action in the courts of the State of Delaware or of the
United States of America located in Wilmington, Delaware, and hereby further
irrevocably and unconditionally waives and agrees not to plead or claim in any
such court that any Action brought in any such court has been brought in an
inconvenient forum.

9.       Waiver and Amendment. Any provision of this Shareholders Agreement may
be waived in writing at any time by the party that is entitled to the benefits
of such provision. This Shareholders Agreement may not be modified, amended,
altered or supplemented except upon the execution and delivery of a written
agreement executed by the Purchaser and the Executives.

10.      Defined Terms. As used herein, the following terms shall be defined as
follows:


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         "Affiliate" shall mean, with respect to any Person, any other Person
that directly or indirectly controls, is controlled by, or is under common
control with such Person.

         "Competitive Activity" shall mean engaging in any of the following
activities: (i) serving as a director of any Competitor; (ii) directly or
indirectly (x) controlling any Competitor or (y) owning any equity or debt
interests in any Competitor (other than equity or debt interests which are
publicly traded and do not exceed 2% of the particular class of interests then
outstanding) (it being understood that, if any such interests in any Competitor
are owned by an investment vehicle or other entity in which the Employee owns an
equity interest, a portion of the interests in such Competitor owned by such
entity shall be attributed to the Employee, such portion determined by applying
the percentage of the equity interest in such entity owned by the Employee to
the interests in such Competitor owned by such entity); (iii) directly or
indirectly soliciting, diverting, taking away, appropriating or otherwise
interfering with any of the customers or suppliers of the Company or any
Affiliate controlled by the Company; or (iv) employment by (including serving as
an officer of), or providing consulting services to, any Competitor.

         "Competitor" shall mean any Person that is engaged in a business
similar to any of the businesses currently or hereafter conducted by the Company
or its subsidiaries (but not including businesses the Company enters into after
the Executive is no longer an employee or director of the Company or any of its
subsidiaries).

         "control" (and the correlative term "controlling") shall mean the
possession, directly or indirectly, of the power to direct or cause the
direction of the management and policies of any Person, whether through the
ownership of equity interests, by contract or otherwise.

         "Governance Termination Event" shall be deemed to have occurred when
either (i) the Purchase Agreement has been amended or Purchaser has waived
compliance therewith, or (ii) Purchaser's ownership of Common Stock has fallen,
in either event such that the Company is not obliged to observe the covenants
set forth in Section 4.1 and 4.10 of the Purchase Agreement.

         "Group" shall mean the Purchaser Group or the Principal Group.

         "Person" shall mean an individual, a corporation, a limited liability
company, a partnership, an association, a trust or any other entity or
organization, including a governmental entity.

         "Principal Group" shall mean the Executives and any Permitted 
Transferees who own any Principal Shares.




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         "Principal Shares" shall mean the 927,801 shares of Common Stock owned
by the Executives as of the date hereof, including any securities issued in
respect thereof as a dividend or stock-split or in a reorganization, merger,
reclassification or otherwise, but excluding any shares of Common Stock
Transferred other than to a Permitted Transferee.

         A "Principal Termination Event" shall be deemed to have occurred when
(i) the Principal Group Transfers (other than to Permitted Transferees) more
than 50% of the Principal Shares owned by the Principals as of the date hereof
(adjusted for any stock splits, stock dividends, recapitalizations and similar
transactions), or (ii) neither Executive is a senior executive or director of
the Company.

         "Purchaser Group" shall mean Purchaser and any Affiliates of Purchaser 
who own any Purchaser Shares.

         "Purchaser Shares" shall mean the shares of Common Stock acquired
pursuant to the Purchase Agreement or the Option Agreement, dated as of the date
hereof, between Purchaser and the Company, including any securities issued in
respect thereof as a dividend or stock-split or in a reorganization, merger,
reclassification or otherwise, but excluding any shares Transferred by Purchaser
other than to Affiliates of Purchaser who agree to be bound by the terms hereof.

         "Specified Shares" shall, at any time, mean with respect to (i) the
Purchaser Group, the Purchaser Shares then owned by the Purchaser Group, and
(ii) the Principal Group, the Principal Shares then owned by the Principal
Group.

         "subsidiary" shall mean, with respect to any Person, any other Person
more than 10% of whose outstanding capital stock or equity interests is owned
directly or indirectly by such Person.



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             IN WITNESS WHEREOF, each of the parties hereto has executed this
Shareholders Agreement as of the date first written above.

                                               PURCHASER:

                                               M & M NOMINEE L.L.C.


                                               By: /s/ Peter Streinger
                                                   -------------------
                                                   Name:  Peter Streinger
                                                   Title: Manager


                                               THE EXECUTIVES:



                                               /s/ Rafael Vaquero Bazan
                                               -------------------------
                                               Rafael Vaquero Bazan


                                               /s/ Fernando Camacho Casas
                                               -------------------------
                                               Fernando Camacho Casas




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             The undersigned partnership agrees to be bound, as if it were an
Executive, by the provisions of the foregoing agreement with respect to the
shares of the Company that it owns.

                                            GARZA JASSO Y ASOCIADOS


                                            By: /s/ Rafael Vaquero Bazan
                                                ------------------------
                                                Name:  Rafael Vaquero Bazan
                                                Title: General Partner

             The undersigned company agrees to be bound, as if it were an
Executive, by the provisions of the foregoing agreement with respect to the
shares of the Company that it owns.

                                            AGROS S.A. DE CV SOCIEDAD DE 
                                            INVESATOR DE CAPITALES


                                            By: /s/ Fernando Camacho Casas
                                                --------------------------
                                                Name:  Fernando Camacho Casas
                                                Title: General Director




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