PETROTECH
HOLDINGS, CORP.


c/o
Valens Capital Management, LLC


335
Madison Avenue, 10th
Floor


New York,
New York 10017




August
15, 2008




XL
TechGroup, Inc.


1901
South Harbor City Blvd., Third Floor


Melbourne,
FL 32901


Attn:
General Counsel




Re:           Letter
Agreement




Gentlemen:




Reference
is made to (i) that certain Letter re: Agreement to Accept Collateral in Partial
Satisfaction of Debt dated as of August 8, 2008 (as amended, modified,
supplemented or restated from time to time, the “Acceptance
Agreement”) by and between PetroTech Holdings, Corp. (“PetroTech”) and XL
TechGroup, Inc. (“XLT”) and(ii)
all agreements, instruments and documents executed and/or delivered in
connection therewith (together with the Acceptance Agreement, each a “Document” and
collectively, the “Documents”).




In
consideration of the consummation of the transactions contemplated by the
Documents, and the agreements set forth herein and for other good and valuable
consideration, the receipt and sufficiency of which are hereby acknowledged, the
parties hereto hereby agree as follows:




1.           PetroTech
hereby acknowledges, confirms and agrees that following the indefeasible
repayment in full in cash of (a) the full amount of any preferred stock
liquidation preference and all accrued dividends thereon to each holder of
preferred stock of PetroTech and (b) the aggregate amount of all obligations,
liabilities and expenses of PetroTech at any time and from time to time owing by
PetroTech to any of Laurus Master Fund, Ltd., Valens Offshore SPV I, Ltd.,
Valens U.S. SPV I, LLC, Valens U.S. SPV I, Ltd., PSource Structured Debt Limited
and all of their respective subsidiaries and affiliates (collectively, the
“Lenders”)
and/or to any other person or entity (the date of any such indefeasible
repayment, the “Repayment Date”),
PetroTech shall, prior to the payment of any dividend or other distribution to
be paid by PetroTech to the holders of common stock of PetroTech from and after
the Repayment Date, pay to XLT fifteen percent (15%) of such dividend or
distribution amounts which would have otherwise been so paid to the holders of
common stock of PetroTech (such 15%, the “XLT Distribution”),
it being understood that (A) no XLT Distribution will be made until the (i)
Repayment Date has occurred, and (ii) all of the equity interests of PetroAlgae,
LLC, DXTech, LLC and Tyratech Inc. held by PetroTech and its affiliates have
been sold or otherwise transferred by PetroTech and its affiliates and any of
such companies not so sold or otherwise transferred shall have been dissolved,
and (B) the sole source of such dividend or distribution shall be from the net
sales proceeds to PetroTech or its affiliates from sales of equity interests in
DXTech, LLC, PetroAlgae, LLC and Tyratech Inc. and any dividends or
distributions paid by such entities to PetroTech or its
affiliates.







2.           XLT
hereby absolutely and unconditionally releases and forever discharges Lenders,
PetroTech, and any and all participants, predecessors, parent corporations,
subsidiary corporations, affiliated corporations, related corporate divisions,
insurers, indemnitors, agents, representatives, consultants, attorneys,
fiduciaries, partners and all successors and assigns thereof, together with all
of the present and former directors, officers, agents and employees of any of
the foregoing, from any and all claims, demands or causes of action of any kind,
nature or description, whether arising in law or equity or upon contract or tort
or under any state or federal law or otherwise, which XLT has had, now has or
has made claim to have against any such person for or by reason of any act,
omission, matter, cause or thing whatsoever arising from the beginning of time
to and including the date of this Letter Agreement, whether such claims, demands
and causes of action are matured or unmatured or known or unknown.




3.           This
Letter Agreement may be executed by the parties hereto in any number of separate
counterparts, and all of said counterparts taken together shall be deemed to
constitute one and the same instrument. Any signature delivered by a party by
facsimile transmission or other electronic transmission shall be deemed to be an
original signature hereto.




4.           THIS
LETTER AGREEMENT AND THE RIGHTS AND OBLIGATIONS OF THE PARTIES UNDER THIS LETTER
AGREEMENT SHALL BE GOVERNED BY, AND CONSTRUED AND INTERPRETED IN ACCORDANCE
WITH, THE INTERNAL LAWS OF THE STATE OF NEW YORK.




[SIGNATURE
PAGES FOLLOW]


2




5.  Any provision
of this Letter Agreement held by a court of competent jurisdiction to be invalid
or unenforceable shall not impair or invalidate the remainder of this Letter
Agreement.





Very
      truly yours,PETROTECH
      HOLDINGS, CORP.By:Name:     
      Patrick ReganTitle: Authorized
      Signatory




The
foregoing is hereby accepted and agreed to this 15thdayof
August, 2008.





XL
      TECHGROUP, INC.By:Name: 
      David P
      SzostakTitle:  
      CFO