Document:

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                                                                    Exhibit 10.4

                                 PROMISSORY NOTE

$216,981.06                                                       April 15, 2001

         After date, without grace, for value received, HOUSTON AMERICAN ENERGY
CORP., a Delaware corporation having its principal office and place of business
in Harris County, Texas (the "Maker") hereby promises to pay to the order of
MOOSE OIL & GAS COMPANY, a Texas corporation having its principal office and
place of business in Harris County, Texas (the "Payee"), the original principal
amount of TWO HUNDRED SIXTEEN THOUSAND NINE HUNDRED EIGHTY-ONE and 06/100
DOLLARS ($216,981.06), together with interest, as hereinafter described. This
Note is payable in lawful money of the United States of America at 801 Travis,
Suite 1425, Houston, Harris County, Texas 77002, or such other place as the
Payee may designate in writing to the Maker.

         The payment of this Note is subject to the terms of that certain
Assignment of Interests in Oil and Gas Leases and Bill of Sale of even date
herewith, between the Maker and the Payee (the "Assignment"), which is
incorporated herein by reference for all purposes.

         This Note shall be due and payable on demand as to both principal and
interest. Interest at a rate of ten percent (10%) per annum shall accrue on the
unpaid principal balance of this Note. If this Note is not paid at maturity,
however maturity may be brought about, all principal due on the date of such
maturity shall bear interest from the date of such maturity at the maximum
contract rate of interest which the Payee may charge the Maker under applicable
law. Interest on this Note shall be computed for the actual number of days
elapsed and on the basis of a year consisting of 360 days.

         If, for any reason whatever, the interest paid on this Note shall
exceed the maximum non-usurious amount permitted by law, the Payee shall refund
to the Maker such portion of said interest as may be necessary to cause the
interest paid on this Note to equal the maximum non-usurious amount permitted by
law, and no more. All sums paid or agreed to be paid to the Payee for the use,
forbearance or detention of the indebtedness evidenced hereby shall to the
extent permitted by applicable law be amortized, prorated, allocated and spread
throughout the full term of this Note until payment in full.

         The Maker shall be entitled to prepay this Note in whole or in part at
any time without the payment of a prepayment premium.

         In the event of default in the payment of this Note or under any
instrument executed in connection with this Note, the Maker agrees to pay on
demand all costs incurred by the Payee (i) in the collection of any sums,
including, but not limited to, principal, interest, expenses, and reimbursements
due and payable on this Note, and (ii) in the enforcement of the other terms and
provisions of this Note or the Assignment, whether such collection or
enforcement be accomplished by suit or otherwise, including the Payee's
reasonable attorney's fees.

         Except as otherwise provided for herein, each maker, surety, guarantor
and endorser of this Note expressly waives all notices, including, but not
limited to, all demands for payment, presentations for payment, notice of
opportunity to cure default, notice of intention to accelerate the maturity,
notice of protest and notice of acceleration of the maturity, notice of protest
and notice of acceleration of the maturity of this Note, and consents that this
Note may be renewed and the time of payment extended without notice and without
releasing any of the parties.

         Any check, draft, money order or other instrument given in payment of
all or any portion of this Note may be accepted by the Payee or any other holder
hereof and handled in collection in the customary manner, but the same shall not
constitute payment hereunder or diminish any rights of the Payee or any other
holder hereof, except to the extent that actual cash proceeds of such instrument
are unconditionally received by the Payee or any other holder hereof and applied
to the indebtedness as herein provided.

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     This Note shall be governed by and construed in accordance with the laws of
the State of Texas and applicable federal law.

                                         HOUSTON AMERICAN ENERGY CORP.

                                         By /s/ John F. Terwilliger
                                           ----------------------------------
                                           John F. Terwilliger, President

                                       2<PAGE>

                                                                    Exhibit 10.5

                         PLAN AND AGREEMENT OF MERGER
                                    BETWEEN
                      OPPORTUNITY ACQUISITION CORPORATION
                                      AND
                         HOUSTON AMERICAN ENERGY CORP.

     Opportunity Acquisition Corporation, a Texas corporation ("OAC"), and
Houston American Energy Corp., a Delaware corporation ("HAEC"), hereby agree as
follows:

     1.   Plan Adopted. A plan of merger merging OAC with and into HAEC (this
          ------------
"Plan of Merger"), pursuant to the provisions of Section 252 of the Delaware
General Corporation Law (the "DGCL"), Article 5.01 of the Texas Business
Corporation Act (the "TBCA") and Section 368(a)(1)(A) of the Internal Revenue
Code, is adopted as follows:

          (a)  OAC shall be merged with and into HAEC, to exist and be governed
by the laws of the State of Delaware.

          (b)  The name of the Surviving Corporation shall be Houston American
Energy Corp. (the "Surviving Corporation").

          (c)  When this Plan of Merger shall become effective, the separate
existence of OAC shall cease and the Surviving Corporation shall succeed,
without other transfer, to all the rights and properties of OAC and shall be
subject to all the debts and liabilities of such corporation in the same manner
as if the Surviving Corporation had itself incurred them. All rights of
creditors and all liens upon the property of each constituent entity shall be
preserved unimpaired, limited in lien to the property affected by such liens
immediately prior to the merger (the "Merger").

          (d)  The Surviving Corporation will be responsible for the payment of
all fees and franchise taxes of the constituent entities payable to the State of
Delaware and the State of Texas, if any.

          (e)  The Surviving Corporation will carry on business with the assets
of OAC, as well as with the assets of HAEC.

          (f)  The Surviving Corporation will be responsible for the payment of
the fair value of shares, if any, required under Article 5.12 of the TBCA or
Section 262 of the DGCL.

          (g)  The shareholders of OAC will surrender all of their shares in the
manner hereinafter set forth.

          (g)  In exchange for the shares of OAC surrendered by its
shareholders, the Surviving Corporation will issue and transfer to such
shareholders on the basis hereinafter set forth, shares of its common stock.

          (h)  The stockholders of HAEC will retain their shares of the
Surviving Corporation.

     2.   Effective Date. The effective date of the Merger (the "Effective
          --------------
          Date") shall be April ___, 2001.

     3.   Submission to Shareholders and Stockholders. This Plan of Merger shall
          -------------------------------------------
be submitted for approval separately to the shareholders of OAC and to the
stockholders of HAEC in the manner provided by the laws of the State of Texas
and the State of Delaware.

     4.   Manner of Exchange. On the Effective Date of the Merger, the
          ------------------
shareholders of OAC shall surrender their stock certificates to HAEC in exchange
for shares of the Surviving Corporation to which they are entitled.

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     5.   Basis of Exchange. The holders of shares of the common stock, no par
          -----------------
value per share, of OAC shall be entitled to receive one (1) share of the common
stock of the Surviving Corporation, par value $0.001 per share, for each such
share of OAC common stock so surrendered.

     6.   Shares of the Surviving Corporation. The presently outstanding
          -----------------------------------
1,000,000 shares of the common stock of HAEC shall remain outstanding as common
stock of the Surviving Corporation.

     7.   Directors and Officers.
          ----------------------

          (a)  The present Board of Directors of HAEC shall continue to serve as
the Board of Directors of the Surviving Corporation until the next annual
meeting or until such time as their successors have been elected and qualified.

          (b)  If a vacancy shall exist on the Board of Directors of the
Surviving Corporation on the Effective Date of the Merger, such vacancy may be
filled by the Board of Directors as provided in the Bylaws of the Surviving
Corporation.

          (c)  All persons who, on the Effective Date of the Merger, are
executive or administrative officers of HAEC shall remain as officers of the
Surviving Corporation until the Board of Directors of the Surviving Corporation
shall otherwise determine. The Board of Directors of the Surviving Corporation
may elect or appoint such additional officers as it may determine.

     8.   Certificate of Incorporation. The Certificate of Incorporation of
          ----------------------------
HAEC, attached hereto as Exhibit A and incorporated herein for all purposes,
existing on the Effective Date of the Merger shall continue in full force as the
Certificate of Incorporation of the Surviving Corporation until altered,
amended, or repealed as provided therein or as provided by law.

     9.   Bylaws. The Bylaws of HAEC, attached hereto as Exhibit B and
          ------
incorporated herein for all purposes, existing on the Effective Date of the
Merger shall continue in full force as the Bylaws of the Surviving Corporation
until altered, amended, or repealed as provided therein or as provided by law.

     10.  Copies of the Plan of Merger. A copy of this Plan of Merger is on file
          ----------------------------
at 801 Travis Street, Suite 1425, Houston, Texas 77002, which is the principal
office of both of the constituent entities. A copy of this Plan of Merger will
be furnished to any member or shareholder of a constituent entity, on written
request and without cost.

     11.  Legal Construction. In case any one or more of the provisions
          ------------------
contained in this Plan of Merger shall for any reason be held to be invalid,
illegal, or unenforceable in any respect, such invalidity, illegality, or
unenforceability shall not affect any other provisions hereof, and this Plan of
Merger shall be construed as if such invalid, illegal, or unenforceable
provision had never been contained herein.

     12.  Benefit. All the terms and provisions of this Plan of Merger shall be
          -------
binding upon and inure to the benefit of and be enforceable by the parties
hereto, and their successors and permitted assigns.

     13.  Law Governing. This Plan of Merger shall be construed and governed by
          -------------
the laws of the State of Delaware, and all obligations hereunder shall be deemed
performable in Harris County, Texas.

     14.  Perfection of Title. The parties hereto shall do all other acts and
          -------------------
things that may be reasonably necessary or proper, fully or more fully, to
evidence, complete or perfect this Plan of Merger, and to carry out the intent
of this Plan of Merger.

     15.  Cumulative Rights. The rights and remedies of any party under this
          -----------------
Plan of Merger and the instruments executed or to be executed in connection
herewith, or any of them, shall be cumulative and the exercise or partial
exercise of any such right or remedy shall not preclude the exercise of any
other right or remedy.

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     16.  Waiver. No course of dealing on the part of any party hereto or its
          ------
agents, nor any failure or delay by any such party with respect to exercising
any right, power or privilege of such party under this Plan of Merger or any
instrument referred to herein shall operate as a waiver thereof, and any single
or partial exercise of any such right, power or privilege shall not preclude any
later exercise thereof or any exercise of any other right, power or privilege
hereunder or thereunder.

     17.  Construction. Whenever used herein, the singular number shall include
          ------------
the plural, the plural number shall include the singular, and the masculine
gender shall include the feminine.

     18.  Multiple Counterparts. This Plan of Merger may be executed in one or
          ---------------------
more counterparts, each of which shall be deemed an original, but all of which
together shall constitute one and the same instrument.

IN WITNESS WHEREOF, the parties have executed this Plan of Merger on April 11,
2001.

                                      OPPORTUNITY ACQUISITION CORPORATION

                                      By /s/ John F. Terwilliger
                                        ----------------------------------------
                                         John F. Terwilliger, President

                                      HOUSTON AMERICAN ENERGY CORP.

                                      By /s/ John F. Terwilliger
                                        ----------------------------------------
                                         John F. Terwilliger, President

Attachments:
-----------
Exhibit A - Certificate of Incorporation of Houston American Energy Corp.
Exhibit B - Bylaws of Houston American Energy Corp.

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                                   EXHIBIT A
                        CERTIFICATE OF INCORPORATION OF
                         HOUSTON AMERICAN ENERGY CORP.
                    (included as Exhibit A to Exhibit 2.1)
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                                   EXHIBIT B
                    BYLAWS OF HOUSTON AMERICAN ENERGY CORP.
                    (included as Exhibit B to Exhibit 2.1)

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