EXHIBIT 10.15





<PAGE>

                          TRADEMARK SECURITY AGREEMENT
                          ----------------------------


         WHEREAS,  Avatar Systems, Inc., a Texas corporation  ("Grantor"),  owns
the Trademarks,  Trademark  registrations,  and Trademark applications listed on
Schedule 1 annexed  hereto,  and is a party to the Trademark  Licenses listed on
Schedule 1 annexed hereto; and

         WHEREAS,  Avatar Systems, Inc., a Texas corporation  ("Borrower"),  and
Bank One,  Texas,  N.A.  ("Lender") are parties to a Loan Agreement  dated as of
July 10, 2000 (as the same may be amended  and in effect from time to time,  the
"Loan Agreement"),  providing for extensions of credit to be made to Borrower by
Lender; and

         WHEREAS,  pursuant to the terms of the Security  Agreement  dated as of
July 10, 2000 (as the same may be amended  and in effect from time to time,  the
"Security  Agreement"),  between Grantor and Lender (in such capacity,  together
with its successors in such capacity, "Grantee"), Grantor has granted to Grantee
a security  interest in  substantially  all the assets of Grantor  including all
right,  title  and  interest  of  Grantor  in,  to and  under  all now owned and
hereafter acquired Trademarks (as defined in the Security Agreement),  Trademark
registrations,  Trademark applications and Trademark Licenses (as defined in the
Security  Agreement),  together with the goodwill of the business  symbolized by
Grantor's  Trademarks,  and all proceeds  thereof,  to secure,  inter alia,  the
payment and performance of the Secured Obligations (as therein defined);

         NOW, THEREFORE,  for good and valuable  consideration,  the receipt and
sufficiency  of which are hereby  acknowledged,  Grantor  does  hereby  grant to
Grantee a  continuing  security  interest in all of Grantor's  right,  title and
interest in, to and under the following (all of the following  items or types of
property being herein collectively  referred to as the "Trademark  Collateral"),
whether presently existing or hereafter created or acquired:

                  (1)  each  Trademark,  Trademark  registration  and  Trademark
         application,  including, without limitation, the Trademarks,  Trademark
         registrations (together with any reissues,  continuations or extensions
         thereof and  Trademark  applications  referred to in Schedule 1 annexed
         hereto,  and all of the goodwill of the business connected with the use
         of, and  symbolized  by, each  Trademark,  Trademark  registration  and
         Trademark application;

                  (2) each  Trademark  License  and all of the  goodwill  of the
         business  connected  with the use of, and symbolized by, each Trademark
         License; and

                  (3) all  products and  proceeds of the  foregoing,  including,
         without  limitation,  any claim by Grantor  against  third  parties for
         past,  present or future (a)  infringement or dilution of any Trademark
         or Trademark registration including, without limitation, the Trademarks
         and Trademark  registrations  referred to in Schedule 1 annexed hereto,
         the  Trademark  registrations  issued  with  respect  to the  Trademark
         applications  referred in Schedule 1 and the Trademarks  licensed under
         any Trademark  License,  or (b) injury to the goodwill  associated with
         any Trademark,  Trademark  registration or Trademark licensed under any
         Trademark License.

TRADEMARK SECURITY AGREEMENT - Page 1


<PAGE>

This security  interest is granted in  conjunction  with the security  interests
granted  to  Grantee  pursuant  to  the  Security   Agreement.   Grantor  hereby
acknowledges and affirms that the rights and remedies of Grantee with respect to
the security  interest in the Trademark  Collateral  made and granted hereby are
more fully set forth in the  Security  Agreement,  the terms and  provisions  of
which are incorporated by reference herein as if fully set forth herein.

         IN  WITNESS  WHEREOF,   Grantor  has  caused  this  Trademark  Security
Agreement to be duly executed by its duly authorized officer thereunto as of the
10" day of July, 2000.

                                         GRANTOR:

                                         AVATAR SYSTEM

(CORPORATE SEAL)                         By:   /s/ Robert C. Shreve, Jr.
                                             --------------------------------
                                             Robert C. Shreve, Jr., President


Acknowledged:



BANK ONE, TEXAS, N.A.



By:     /s/ Reed V. Thompson
    ---------------------------
    Reed V. Thompson, President






TRADEMARK SECURITY AGREEMENT - Page 2

<PAGE>

                                 ACKNOWLEDGMENT

STATE OF                                  ss.
         ---------------------------
                                          ss.
COUNTY OF                                 ss.
          --------------------------

         On the _____ day of ______________, 2000, before me personally appeared
_____________________,  to me  personally  known or proved to me on the basis of
satisfactory  evidence  to be the  person  described  in and  who  executed  the
foregoing instrument as ___________________ of ______________________, who being
by me duly  sworn,  did  depose  and say  that  he is  _____________________  of
______________________,  the  described  in and  which  executed  the  foregoing
instrument; that he knows the seal of said corporation; that the seal affixed to
said  instrument is such corporate seal; that the said instrument was signed and
sealed on behalf of said corporation by order of its Board of Directors; that he
signed his name thereto by like order; and that he acknowledged  said instrument
to be the free act and deed of said corporation.



(Seal)                                               ---------------------------
                                                     Notary Public







TRADEMARK SECURITY AGREEMENT - Page 3

<PAGE>

                                 ACKNOWLEDGMENT

STATE OF                                  ss.
         ---------------------------
                                          ss.
COUNTY OF                                 ss.
          --------------------------

         On the _____ day of ______________, 2000, before me personally appeared
_____________________,  to me  personally  known or proved to me on the basis of
satisfactory  evidence  to be the  person  described  in and  who  executed  the
foregoing  instrument as Vice President of Bank One, Texas, N.A. who being by me
duly sworn,  did depose and say that he is Vice  President  of Bank One,  Texas,
N.A.,  the national  banking  association  described  in and which  executed the
foregoing  instrument;  that the said instrument was signed and sealed on behalf
of said  national  banking  association  under  due  authority  granted  by such
national banking association; that he signed his name thereto by like order; and
that he  acknowledged  said  instrument  to be the  free  act  and  deed of said
national banking association.



(Seal)                                               ---------------------------
                                                     Notary Public






TRADEMARK SECURITY AGREEMENT - Page 4


<PAGE>

                                   Schedule 1
                                  to Trademark
                               Security Agreement

                      UNITED STATES TRADEMARK REGISTRATIONS

                                               Registration   Registration
        Grantor         Mark      Country          Number         Date
        -------         ----      -------          ------         ----
                                            None.


                      UNITED STATES TRADEMARK APPLICATIONS
                      ------------------------------------

                   Mark                           Application Serial No.
                   ----                           ----------------------
                   AVATAR                         75-614, 378

                   PETROWARE                      75-623, 916

                   PETROWARE 2000                 75-894, 228

                   PETROWARE PLUS                 75-894, 236


                         FOREIGN TRADEMARK REGISTRATIONS
                         -------------------------------

                                      None.



                         FOREIGN TRADEMARK APPLICATIONS
                         ------------------------------

                                      None.



                               TRADEMARK LICENSES
                               ------------------

                                      None.



                             UNREGISTERED TRADEMARKS
                             -----------------------

                                      None.





TRADEMARK SECURITY AGREEMENT - Page 5