<PAGE>
                                                                     EXHIBIT 4.3

                                                                       EXHIBIT A

                       FORM OF FACE OF EXCHANGE SECURITY
                          OR PRIVATE EXCHANGE SECURITY

              */**/








----------
*/If the Security is to be issued in global form add the Global Securities
Legend from Exhibit 1 to Appendix A and the attachment from such Exhibit 1
captioned "TO BE ATTACHED TO GLOBAL SECURITIES - SCHEDULE OF INCREASES OR
DECREASES IN GLOBAL SECURITY".]

**/If the Security is a Private Exchange Security issued in a Private Exchange
to an Initial Purchaser holding an unsold portion of its initial allotment, add
the Restricted Securities Legend from Exhibit 1 to Appendix A and replace the
Assignment Form included in this Exhibit A with the Assignment Form included in
such Exhibit 1.

<PAGE>


                                                                             167



No.                                                                      $______

                          11 3/8% Senior Notes Due 2011


         CITGO Petroleum Corporation, a Delaware corporation, promises to pay to
__________, or registered assigns, the principal sum of _______________ Dollars
on February 1, 2011.

         Interest Payment Dates: February 1 and August 1, commencing __________.

         Record Dates: January 15 and July 15.

         Additional provisions of this Security are set forth on the other side
of this Security.

Dated:

                                       CITGO PETROLEUM CORPORATION,

                                       By:
                                          --------------------------------------
                                          Name:
                                          Title:


                                       By:
                                          --------------------------------------
                                          Name:
                                          Title:

TRUSTEE'S CERTIFICATE OF
     AUTHENTICATION
<PAGE>
                                                                             168


THE BANK OF NEW YORK
  as Trustee, certifies
       that this is one of
       the Securities referred
       to in the Indenture.

  by
    --------------------------
        Authorized Signatory

<PAGE>
                                                                             169


                   [FORM OF REVERSE SIDE OF EXCHANGE SECURITY
                         OR PRIVATE EXCHANGE SECURITY]]

                          11 3/8% Senior Note Due 2011

1. Interest

         CITGO Petroleum Corporation a Delaware corporation (such corporation,
and its successors and assigns under the Indenture hereinafter referred to,
being herein called the "Company"), promises to pay interest on the principal
amount of this Security at the rate per annum shown above. The Company will pay
interest semiannually in arrears on February 1 and August 1 of each year,
commencing on ______________. Interest on the Securities will accrue from the
most recent date to which interest has been paid or, if no interest has been
paid, from the date of original issuance. The Company will pay interest on
overdue principal at 1% per annum in excess of the above rate and will pay
interest on overdue installments of interest at this higher rate to the extent
lawful. Interest will be computed on the basis of a 360-day year of twelve
30-day months.

2. Method of Payment

         The Company will pay interest on the Securities (except defaulted
interest) to the Persons who are registered holders of Securities at the close
of business on the January 15 or July 15 next preceding the interest payment
date even if Securities are canceled after the record date and on or before the
interest payment date. Holders must surrender Securities to a Paying Agent to
collect principal payments. The Company will pay


<PAGE>
                                                                             170


principal and interest in money of the United States that at the time of payment
is legal tender for payment of public and private debts. Payments in respect of
the Securities represented by a Global Security (including principal, premium,
if any, and interest) will be made by wire transfer of immediately available
funds to the accounts specified by The Depository Trust Company. The Company
will make all payments in respect of a certificated Security (including
principal, premium, if any, and interest) by mailing a check to the registered
address of each Holder thereof; provided, however, that payments on a
certificated Security will be made by wire transfer to a U.S. dollar account
maintained by the payee with a bank in the United States if such Holder elects
payment by wire transfer by giving written notice to the Trustee or the Paying
Agent to such effect designating such account no later than 30 days immediately
preceding the relevant due date for payment (or such other date as the Trustee
may accept its discretion).

3. Paying Agent and Registrar

         Initially, The Bank of New York, a New York banking corporation (the
"Trustee"), will act as Paying Agent and Registrar. The Company may appoint and
change any Paying Agent, Registrar or co-registrar without notice. The Company
or any of its domestically incorporated Wholly Owned Subsidiaries may act as
Paying Agent, Registrar, co-registrar or transfer agent.


4. Indenture

         The Company issued the Securities under an Indenture dated as of
February 27, 2003 ("Indenture"), between the Company and the Trustee. The terms
of the Securities include those stated in the Indenture and those made part of
the Indenture by reference to the Trust Indenture Act of 1939 (15 U.S.C.
Sections 77aaa-77bbbb) as in effect on the date of the Indenture (the "Act").
Terms defined in the Indenture and not defined herein have the meanings ascribed
thereto in the Indenture. The Securities are subject to all such terms, and
Securityholders are referred to the Indenture and the Act for a statement of
those terms.


<PAGE>

                                                                             171

         The Securities are general senior unsecured obligations of the Company.
The Company shall be entitled, subject to its compliance with Section 4.03 of
the Indenture, to issue Additional Securities pursuant to Section 2.13 of the
Indenture. The Initial Securities issued on the Issue Date, any Additional
Securities and all Exchange Securities or Private Exchange Securities issued in
exchange therefor will be treated as a single class for all purposes under the
Indenture. The Indenture contains covenants that limit the ability of the
Company and its Restricted Subsidiaries to incur additional indebtedness; pay
dividends or distributions on, or redeem or repurchase capital stock; make
investments or other restricted payments; issue or sell capital stock of
Restricted Subsidiaries; engage in transactions with affiliates; create liens
on assets; transfer or sell assets; guarantee indebtedness; pay dividends or
other payments of Restricted Subsidiaries; consolidate, merge or transfer all
or substantially all of its assets and the assets of its subsidiaries; and
engage in sale/leaseback transactions. These covenants are subject to import
exceptions and qualifications and cease to apply or are modified upon and after
the occurrence of an Investment Grade Rating Event.

5. Optional Redemption

         Except as set forth below, the Company shall not be entitled to redeem
the Securities at its option prior to their stated maturity of February 1, 2011.

         On and after February 1, 2007, the Company shall be entitled at its
option to redeem all or a portion of the Securities upon not less than 30 nor
more than 60 days' notice, at the redemption prices (expressed as percentages of
principal amount, on the redemption date) plus accrued and unpaid interest to
the redemption date (subject to the right of Holders of record on the relevant
record date to receive interest due on the relevant interest payment date), if
redeemed during the 12-month period commencing on February 1 of the years set
forth below:

<Table>
<Caption>
                                          Redemption
                    Period                  Price
                    ------                ----------
<S>                                       <C>
             2007 ....................       105.688%
             2008 ....................       102.843
</Table>
<PAGE>

                                                                             172

                  2009 and thereafter...                100.00

         Prior to February 1, 2006, the Company may at its option on one or
more occasions redeem Securities (which includes Additional Securities, if any)
in an aggregate principal amount not to exceed 35% of the aggregate principal
amount of the Securities (which includes Additional Securities, if any)
originally issued at a redemption price (expressed as a percentage of principal
amount) of 111 3/8%, plus accrued and unpaid interest to the redemption date,
with the net cash proceeds from one or more Equity Offerings subsequent to the
Issue Date; provided, however, that (1) at least 65% of such aggregate
principal amount of Securities (which includes Additional Securities, if any)
remains outstanding immediately after the occurrence of each such redemption
(other than Securities held, directly or indirectly, by the Company or its
Affiliates); and (2) each such redemption occurs within 60 days after the date
of the related Public Equity Offering.

         Prior to February 1, 2007 the Company may at its option redeem all,
but not less than all, of the Securities at a redemption price equal to 100% of
the principal amount of the Securities plus the Applicable Premium as of, and
accrued and unpaid interest to, the redemption date (subject to the right of
Holders on the relevant record date to receive interest due on the relevant
interest payment date). Notice of such redemption must be mailed by first-class
mail to each Holder's registered address, not less than 30 nor more than 60
days prior to the redemption date.

         "Applicable Premium" means, with respect to a Security at any
redemption date, the greater of (i) 1.00% of the principal amount of such
Security and (ii) the excess of (A) the present value at such redemption date
of (1) the redemption price of such Security on February 1, 2007 (such
redemption price being described in the second paragraph of this paragraph 5
exclusive of any accrued interest) plus (2) all required remaining scheduled
interest payments due on such Security through 2007, computed using a discount
rate equal to the Adjusted Treasury Rate, over (B) the principal amount of such
Security on such redemption date.

         "Adjusted Treasury Rate" means, with respect to any redemption date,
(i) the yield, under the heading which represents the average for the
immediately preceding week,


<PAGE>

                                                                             173



appearing in the most recently published statistical release designated "H.15
(519)" or any successor publication which is published weekly by the Board of
Governors of the Federal Reserve System and which establishes yields on actively
traded United States Treasury securities adjusted to constant maturity under the
caption "Treasury Constant Maturities," for the maturity corresponding to the
Comparable Treasury Issue (if no maturity is within three months before or after
February 1, 2007, yields for the two published maturities most closely
corresponding to the Comparable Treasury Issue shall be determined and the
Adjusted Treasury Rate shall be interpolated or extrapolated from such yields on
a straight line basis, rounding to the nearest month) or (ii) if such release
(or any successor release) is not published during the week preceding the
calculation date or does not contain such yields, the rate per year equal to the
semi-annual equivalent yield to the maturity of the Comparable Treasury Issue
(expressed as a percentage of its principal amount) equal to the Comparable
Treasury Price for such redemption date, in each case calculated on the third
Business Day immediately preceding the redemption date, plus 0.50%.

         "Comparable Treasury Issue" means the United States Treasury security
selected by the Quotation Agent as having a maturity comparable to the remaining
term from the redemption date to February 1, 2007, that would be utilized, at
the time of selection and in accordance with customary financial practice, in
pricing new issues of corporate debt securities of a maturity most nearly equal
to February 1, 2007.

         "Comparable Treasury Price" means, with respect to any redemption date,
if clause (ii) of the Adjusted Treasury Rate is applicable the average of three,
or such lesser number as is obtained by the Trustee, Reference Treasury Dealer
Quotations for such redemption date.

         "Quotation Agent" means the Reference Treasury Dealer selected by the
Trustee after consultation with the Company.

         "Reference Treasury Dealer" means Credit Suisse First Boston LLC and
its successors assigns, and two other nationally recognized investment banking
firms selected by the Company that are primary U.S. Government securities
dealers.

         "Reference Treasury Dealer Quotations" means, with respect to each
Reference Treasury Dealer and any redemption date, the average, as determined by
the Trustee, of the bid and asked
<PAGE>


                                                                             174



prices for the Comparable Treasury Issue, expressed in each case as a percentage
of its principal amount, quoted in writing to the Trustee by such Reference
Treasury Dealer at 5:00 p.m., New York City Time, on the third Business Day
immediately preceding such redemption date.

6. Notice of Redemption

         Notice of redemption will be mailed at least 30 days but not more than
60 days before the redemption date to each Holder of Securities to be redeemed
at his registered address. Securities in denominations larger than $1,000
principal amount may be redeemed in part but only in whole multiples of $1,000.
If any Security is redeemed in part only, the notice of redemption that relates
to that Security will state the portion of the principal amount thereof to be
redeemed. The Company will issue a new Security in a principal amount equal to
the unredeemed portion of the original Security in the name of the Holder upon
cancelation of the original Security. If money sufficient to pay the redemption
price of and accrued interest on all Securities (or portions thereof) to be
redeemed on the redemption date is deposited with the Paying Agent on or before
the redemption date and certain other conditions are satisfied, on and after
such date interest ceases to accrue on such Securities (or such portions
thereof) called for redemption.

7. Put Provisions

         Upon a Change of Control, any Holder of Securities will have the right
to cause the Company to repurchase such Holder's Securities at a repurchase
equal to 101% of the principal amount of the Securities to be repurchased plus
accrued interest to the date of repurchase (subject to the right of holders of
record on the relevant record date to receive interest due on the related
interest payment date) as provided in, and subject to the terms of, the
Indenture.

         Under certain circumstances as set forth in the Indenture, the Company
will be required to offer to purchase Securities with the Net Available Cash
from an Asset Disposition.
<PAGE>
                                                                             175


8. Denominations; Transfer; Exchange

         The Securities are in registered global form without coupons in minimum
denominations of $1,000 principal amount and whole multiples of $1,000. A holder
may transfer or exchange Securities in accordance with the Indenture. The
Registrar may require a Holder, among other things, to furnish appropriate
endorsements or transfer documents and to pay any taxes and fees required by law
or permitted by the Indenture. The Registrar need not register the transfer of
or exchange any Securities selected for redemption (except, in the case of a
Security to be redeemed in part, the portion of the Security not to be redeemed)
or any Securities for a period of 15 days before a selection of Securities to be
redeemed or 15 days before an interest payment date.


9. Persons Deemed Owners

         The registered Holder of this Security may be treated as the owner of
it for all purposes.

10. Unclaimed Money

         If money for the payment of principal or interest remains unclaimed for
two years, the Trustee or Paying Agent shall pay the money back to the Company
at its request unless an abandoned property law designates another Person. After
any such payment, Holders entitled to the money must look only to the Company
and not to the Trustee for payment.

11. Discharge and Defeasance

         Subject to certain conditions, the Company at any time shall be
entitled to terminate some or all of its obligations under the Securities and
the Indenture if the Company deposits with Trustee money or U.S. Government
Obligations for the payment of principal and interest on the Securities to
redemption or maturity, as the case my be.

12. Amendment, Waiver


<PAGE>

                                                                             176


         Subject to certain exceptions set forth in the Indenture, (i) the
Indenture and the Securities may be amended with the written consent of the
Holders of at least a majority in principal amount outstanding of the Securities
and (ii) any default or noncompliance with any provision may be waived with the
written consent of the Holders of a majority in principal amount outstanding of
the Securities. Subject to certain exceptions set forth in the Indenture,
without the consent of any Securityholder, the Company and the Trustee shall be
entitled to amend the Indenture or the Securities to cure any ambiguity,
omission, defect or inconsistency, or to comply with Article 5 of the Indenture,
or to provide for uncertificated Securities in addition to or in place of
certificated Securities, or to add guarantees with respect to the Securities or
to secure the Securities, or to add additional covenants or surrender rights and
powers conferred on the Company, or to comply with any requirements of the SEC
in connection with qualifying, or maintaining the qualification of, the
Indenture under the Trust Indenture Act, or to make change that does not
adversely affect the rights of any Securityholder.

13. Defaults and Remedies

         Under the Indenture, Events of Default include (i) default for 30 days
in payment of interest on the Securities; (ii) default in payment of principal
on the Securities at maturity, upon redemption pursuant to paragraph 5 of the
Securities, upon acceleration or otherwise, or failure by the Company to redeem
or purchase Securities when required; (iii) failure by the Company to comply
with other agreements in the Indenture or the Securities, in certain cases
subject to notice and lapse of time: (iv) certain accelerations (including
failure to pay within any grace period after final maturity) of other
Indebtedness of the Company if the amount accelerated (or so unpaid) exceeds $35
million; (v) certain events of bankruptcy or insolvency with respect to the
Company and the Significant Subsidiaries; and (vi) certain judgments or decrees
for the payment of money in excess of $35 million. If an Event of Default occurs
and is continuing, the Trustee or the Holders of at least 25% (or 12.5% in the
case of a failure to comply with


<PAGE>
                                                                             177

Section 4.04 of the Indenture) in principal amount of the Securities may declare
all the Securities to be due and payable immediately. Certain events of
bankruptcy or insolvency are Events of Default which will result in the
Securities being due and payable immediately upon the occurrence of such Events
of Default.

         Securityholders may not enforce the Indenture or the Securities except
as provided in the Indenture. The Trustee may refuse to enforce the
Indenture or the Securities unless it receives indemnity or security
satisfactory to it. Subject to certain limitations, Holders of a majority in
principal amount of the Securities may direct the Trustee in its exercise of any
trust or power. The Trustee may withhold from Securityholders notice of any
continuing Default (except a Default in payment of principal or interest) if it
determines that withholding notice is in the interest of the Holders.

14. Trustee Dealings with the Company

         Subject to certain limitations imposed by the Act, the Trustee under
the Indenture, in its individual or any other capacity, may become the owner or
pledge of Securities and may otherwise deal with and collect obligations owed to
it by the Company or its Affiliates and may otherwise deal with the Company or
its Affiliates with the same rights it would have if it were not trustee.

15. No Recourse Against Others

         A director, officer, employee or stockholder, as such, of the Company
or the Trustee shall not have any liability for any obligations of the Company
under the Securities or the Indenture or for any claim based on, in respect of
or by reason of such obligations or their creation. By accepting a Security,
each Securityholder waives and releases all such liability. The waiver and
release are part of the consideration for the issue of the Securities.

<PAGE>


                                                                             178



16. Authentication

         This Security shall not be valid until an authorized signatory of the
Trustee (or an authenticating agent) manually signs the certificate of
authentication on the other side of this Security.

17. Abbreviations

         Customary abbreviations may be used in the name of a Securityholder or
an assignee, such as TEN COM (=tenants in common), TEN ENT (=tenants by the
entireties), JT TEN (=joint tenants with rights of survivorship and not as
tenants in common), CUST (=custodian), and U/G/M/A (=Uniform Gift to Minors
Act).

18. CUSIP Numbers

         Pursuant to a recommendation promulgated by the Committee on Uniform
Security Identification Procedures the Company has caused CUSIP numbers to be
printed on the Securities and has directed the Trustee to use CUSIP numbers in
notices of redemption as a convenience to Securityholders. No representation is
made as to the accuracy of such numbers either as printed on the Securities or
as contained in any notice of redemption and reliance may be placed only on the
other identification numbers placed thereon.

19. Governing Law

         THIS SECURITY SHALL BE GOVERNED BY, AND CONSTRUED IN ACCORDANCE WITH,
THE LAWS OF THE STATE OF NEW YORK BUT WITHOUT GIVING EFFECT TO APPLICABLE
PRINCIPLES OF CONFLICTS OF THE LAW TO THE EXTENT THAT THE APPLICATION OF THE
LAWS OF ANOTHER JURISDICTION WOULD BE REQUIRED THEREBY.

         The Company will furnish to any Securityholder upon written request and
without charge to the Security holder a copy of the Indenture which has in it
the text of this Security in larger type. Requests may be made to:

         CITGO Petroleum Corporation
         One Warren Place

<PAGE>


                                                                             179



         6100 South Yale Avenue
         Tulsa, Oklahoma 74136

         Attention: Corporate Secretary
<PAGE>


                                                                             180




--------------------------------------------------------------------------------

                                                                 ASSIGNMENT FORM

To assign this Security, fill in the form below:

I or we assign and transfer this Security to


         (Print or type assignee's name, address and zip code)

         (Insert assignee's soc. sec. or tax I.D. No.)


and irrevocably appoint                              agent to transfer this
Security on the books of the Company. The agent may substitute another to act
for him.



--------------------------------------------------------------------------------

Date:               Your Signature:
     ----------                    ---------------------------------------------



--------------------------------------------------------------------------------
Sign exactly as your name appears on the other side of this Security.
<PAGE>




                       OPTION OF HOLDER TO ELECT PURCHASE

         If you want to elect to have this Security purchased by the Company
pursuant to Section 4.06 or 4.09 of the Indenture, check the box:

                                      [ ]

         If you want to elect to have only part of this Security purchased by
the Company pursuant to Section 4.06 or 4.09 of the Indenture, state the amount
in principal amount:  $


Date:               Your Signature:
     ----------                    ---------------------------------------------
                                   (Sign exactly as your name appears on the
                                    other side of this Security.)

Signature Guarantee:
                    ------------------------------------------------------------
                                   (Signature must be guaranteed)


         Signatures must be guaranteed by an "eligible guarantor institution"
meeting the requirements of the Registrar, which requirements include membership
or participation in the Security Transfer Agent Medallion Program ("STAMP") or
such other "signature guarantee program" as may be determined by the Registrar
in addition to, or in substitution for, STAMP, all in accordance with the
Securities Exchange Act of 1934, as amended.