<PAGE>

EXHIBIT 10.20


                            INGEN TECHNOLOGIES, INC.

                            STOCK PURCHASE AGREEMENT

THIS STOCK PURCHASE AGREEMENT (The "Agreement") is made and entered into this
15th day of October, 2004; by and between KHOO Yong Sin (the "Purchaser"), a an
Individual representing various investment groups, having its principal
offices/location at No. 21 Upper Weld Road, Singapore 207378, and Ingen
Technologies. Inc. (the "Seller", "Ingen" or the "Company"), a Goergia
corporation, having its corporate headquarters at 285 E. County Line Rd.,
Calimesa CA 92320;

                              W I T N E S S E T H:

         WHEREAS, the Seller has the authority to issue 5,000,000 shares (five
Million shares) of the Company's public common stock that is Registered and
Restricted under SEC Rule-144; and

         WHEREAS, the Seller is in the business of developing, manufacturing,
marketing and selling medical and commercial products; and

         WHEREAS, the Seller is desirous of selling shares of its common stock
at negotiated prices to sophisticated and knowledgeable investors for the
purpose of raising working capital and expanding its business in accordance with
its business plan; and


                                  Page 1 of 11
<PAGE>

         WHEREAS, the Purchaser is representing various investors and interested
in purchasing common shares of the Company's stock in accordance with the terms
and conditions set forth herein,

         WHEREAS, the parties hereto desire to set forth in writing their
understandings and agreements;

NOW, THEREFORE, in consideration of the following premises, representations,
warranties, covenants, and for other good and valuable consideration, the timely
receipt and sufficiency of which are hereby acknowledged, the parties hereto,
intending to be legally bound, agree as follows:

1.       Sale of Shares
         --------------

Pursuant to the terms contained in this Agreement, the Purchaser hereby agrees
that it will tender the purchase price (the "Purchase Price") of $0.05 (Five
Cents) to buy up to 5,000,000 (Five Million) shares (the "Shares") of public
common stock issued by the Company and Restricted under Rule-144 pursuant to the
purchase schedule in Exhibit-A and made a part hereof. The total amount of
purchase being $ 250,000 (Two Hundred Fifty Thousand Dollars). This sum shall be
tendered in certified funds (cashier check or bank draft) and/or a wire transfer
to the bank account of the Company pursuant to the payment schedule attached and
made a part of herein as Exhibit-A. With the simultaneous payment and delivery
of the Purchase Price by the Purchaser to the Company, the Seller shall issue
and deliver to the Company immediate tender for the said shares of common stock
referenced herein for value of the purchase amount received by the Purchaser.
The Company shall be responsible for assuring that the purchased shares are duly
recorded with the Stock Transfer Agent referred to as Executive Registrar and
Transfer Agency, Inc., located in Englewood, Colorado, and as fully assessable
and paid stock in the corporate stock register and with the records of the
Company's stock transfer agent. Said event shall hereinafter be known as the
"Closing."


                                  Page 2 of 11
<PAGE>

All parties further acknowledge that they have had the opportunity to hire
counsel of their own choosing to serve as counselors and advisors in this
transaction.

2.       Representations and Warranties of Seller.
         -----------------------------------------

As a material inducement to Purchaser to enter into this Agreement, Seller
hereby makes the following representations and warranties, effective as of the
date hereof and AT Closing;

(a) The execution and delivery of this Agreement and the consummation of the
transaction contemplated hereby does not, and as of Closing shall not, violate
any provision of any existing law or regulation, or any mortgage, indenture,
security agreement, contract, or other agreement to which Seller is a party.

(b) Seller has the full, absolute, and entire power and legal rights to execute,
deliver and perform this Agreement and to consummate the transaction
contemplated hereby.

(c) The Shares to be sold to Purchaser are free and clear of all liens and other
encumbrances.

(d) Each share sold by the Seller to the Purchaser pursuant to this Agreement
shall be a validly issued, fully paid and nonassessable share of unrestricted
common stock of the Corporation.

(e) The Company is a corporation duly incorporated, organized, validly existing
and in good standing under the laws of its' jurisdiction of incorporation and
the Company has the requisite corporate power to carry on its business as now
being conducted.


                                  Page 3 of 11
<PAGE>

(1) The Seller makes no warranties and representations whatsoever, whether
express or implied, either directly or indirectly, pertaining to the market
value of the Shares or the Company. The Purchaser's decision to buy the Shares
referenced herein are the result of the Purchaser's own due diligence, research
and investigation. The Purchaser acknowledges that it has been advised by the
Company that there currently exists no public market for the sale of its Shares,
The value of the Company and its equities will in the future depend upon
circumstances that are, in many instances, within the control of the Company or
its officers and directors. These factors include, but are not limited to, the
public's perception of and need for the Company's products, the types and prices
of competing products, AND the ability of the Company to implement its business
plan.

3.       Representations and Warranties of Purchaser
         -------------------------------------------

As a material inducement to Seller to enter into this Agreement, Purchaser
Hereby make the following representations and warranties, effective as of the
date hereof and at Closing:

(a) The execution and delivery of this Agreement and the consummation of the
transaction contemplated hereby does not, and as of Closing shall not violate
any provision of any existing law or regulation, or any mortgage, indenture,
security agreement, contact, or other agreement to which Purchaser is a party.

(b) Purchaser has the full, absolute, and entire power and legal right to
execute, deliver and perform Ibis Agreement and to consummate the transaction
contemplated hereby.

(c) Purchaser has sufficient knowledge and experience in investing in companies
similar to the Corporation, in terms of the Corporation's stage of development,
so as to be able to evaluate the risks and merits of its investment in the
Seller's Shares, and it is able financially to bear the risks thereof


                                  Page 4 of 11
<PAGE>

(d) Purchaser has undertaken all due diligence which it deemed necessary or
appropriate and, in furtherance thereof, has had an opportunity to discuss with
the Seller all material aspects and conditions of the Corporation, including the
management and financial affairs of the Corporation, and to obtain information
and examine all documents relating to the Corporation. All questions asked by
the Purchaser have been answered to its full satisfaction, and all information
and documents, records and books pertaining to this investment the Purchaser has
requested have been made available to it.

(e) The Shares being purchased by Purchaser are being provided to various
investors, and as such the Purchaser shall provide instructions to the Seller
regarding issuing the shares in each of the names of the investors. The
Purchaser shall provide the Seller the name in which the certificate should be
issued, the amount of shares to be issued, the address and tax identification of
the name in which the shares are to be issued.

(f) Purchaser understands that the Seller is a public company. Accordingly,
Purchaser understands and acknowledges that the Shares are registered under the
Securities Act of 1933 (the "Act") pursuant to Section 4(2) thereof or Rule 505
and Rule 506 promulgated under the Act.

(g) Purchaser recognizes that an investment in the Shares involves a degree of
risk, and it is fully cognizant of and understands all of the risk factors
related to the purchase of the Shares, and Purchaser has negotiated the terms
and conditions of this Agreement in consideration thereof.

(h) Purchaser warrants and represents that it has had the opportunity to retain
counsel of its' own choosing to advise it and to review and negotiate the terms
and conditions of this transaction.


                                  Page 5 of 11
<PAGE>

4.       Conditions Precedent to the Obligations of Purchaser.
         -----------------------------------------------------

All obligations of Purchaser to close on the sale and purchase pursuant to this
Agreement shall be subject to the following conditions:

(a) The Seller shall deliver to the Transfer Agent within the time stipulated in
this Agreement the certificates representing the Shares.

(b) The Stockholders of the Corporation representing a majority of shares
authorized and issued shall consent to the execution by Seller of this
Agreement.

(c) In the event that the Purchaser is not able to meet or complete the Purchase
Schedule in Exhibit-A, the Seller may terminate this Agreement by serving
written notice to the Purchaser and the termination shall be effective seven (7)
days from the date of said written notice. Upon termination, either party shall
not have any claims against the other party.

5.       Expenses.
         ---------

Each party hereto shall pay its own expenses in connection with the transaction
contemplated hereby, whether or not such transaction shall be consummated.

6.       Brokerage.
         ----------

Each party hereto will indemnify and hold harmless the other from and in respect
to any claim for brokerage or other commissions relative to this Agreement or to
the transactions contemplated hereby, based in any way on agreements,
arrangements or understandings made & claimed to have been made by such party
with any third party.


                                  Page 6 of 11
<PAGE>

7.       Assignability.
         --------------

This Agreement and the burdens and benefits hereunder are not assignable by
either party without the prior written consent of the other party. The Seller
understands that the Purchaser is representing various investors, and therefore
the Seller authorizes the Purchaser to provide instructions regarding the name
in which each share certificate should be issued. The Purchaser will represent
each of his investors under the terms and conditions herein.

8.       Notices.
         --------

All notices, requests, consents and other communications hereunder shall be in
writing and shall be delivered in person or by overnight courier (with proof of
receipt requested) or mailed by certified or registered mail, return receipt
requested, addressed as follows:

(a) If to the Seller, to Scott Sand, Chairman of Ingen Technologies, Inc.

(b) If to the Purchaser, to or at such other address or addresses as shall have
been furnished by one party to the other in the manner specified in this
paragraph 8.

9.       Governing Law.
         --------------

This Agreement shall be governed by and construed in accordance with the laws of
the State of Georgia without giving effect to the conflict of law provisions
thereof.

10.      Headings.
         ---------

The descriptive headings of the several provisions and sections of this are
inserted for convenience only and do not constitute a part of this Agreement.


                                  Page 7 of 11
<PAGE>

11.      Entire Agreement.
         -----------------

This Agreement including the Exhibits hereto constitutes the entire agreement of
the parties with respect to the subject matter hereof. All Exhibits hereto are
incorporated herein by reference.

12.      Counterparts.
         -------------

This Agreement may be executed in two or more counterparts, each of which shall
be deemed an original, but all of which together shall constitute one and the
same instrument.

13.      Changes and Waiver.
         -------------------

No change or modification of this Agreement shall be valid unless the same is in
writing and signed by all parties. No waiver of any provision of this Agreement
shall be valid unless in writing and signed by the person against whom the
provision is sought to be enforced. The failure of any party at any time to
insist upon strict performance of any condition, promise, agreement or
understanding set forth herein shall not be construed as a waiver or
relinquishment of the right to insist upon strict performance of the same or any
other condition, promise, agreement or understanding at a future time.

14.      Survival of Representations and Warranties.
         -------------------------------------------

All of the representations and warranties contained in this Agreement shall
survive (i) the execution of this Agreement and any other documents related
thereto and (ii) the transfer of the Shares to the Escrowee and ultimately to
the Purchaser and shall not be merged therein.


                                  Page 8 of 11
<PAGE>

15.      Invalid Provisions.
         -------------------

Should any portion of this Agreement be declared invalid or unenforceable for
any reason, it shall be modified and adjusted rather than voided, if possible to
achieve the material intent of the parties. Any invalidity of any provision of
this Agreement shall not affect any other provisions of this Agreement, which
shall be deemed enforceable and valid to the maximum extent possible.

16.      Facsimiles.
         -----------

Facsimile or email transmissions of this Agreement, when duly executed by the
parties or their authorized representatives shall be as effective and legally
binding as executed originals of this Agreement.

17.      Exhibits to the Agreement.
         --------------------------

The following documents have been provided to the Purchaser and shall be deemed
to be part of this Agreement and are furnished by the Seller to the Purchaser to
inform it of the Company's activities and plans.

i)       Corporate Charter
ii)      Certificate of Good Standing
iii)     Financial Statement
iv)      Tax Returns
v)       Patents & Trademarks


                                  Page 9 of 11
<PAGE>

         IN WITNESS WHEREOF, the parties hereto have executed this Agreement on
the year and date first written above.



          Purchaser:

          /S/ KHOO Yong Sin                                    October 15, 2004
          -------------------------------------------          ----------------
          KHOO Yong Sin                                              Date
          No. 21 Upper Weld Road
          Singapore, 207378
          Tel: +65 9746 8288



          Ingen Technologies, Inc.

          /S/ SCOTT R. SAND                                    October 15, 2004
          -------------------------------------------          ----------------
          Scott R. Sand, Chairman and CEO                            Date


                                 Page 10 of 11
<PAGE>

                                    EXHIBIT-A

PURCHASE SCHEDULE:


The Purchaser agrees to pay $50,000 on or before November 15, 2004

The Purchaser agrees to pay $100,000 on or before December 15, 2004

The Purchaser agrees to pay $100,000 on or before January 15, 2005


                                 Page 11 of 11