<PAGE>
                                                                    Exhibit 4.19



           THIRD AMENDMENT TO LOAN AND SECURITY AGREEMENT AND WAIVER


     THIS THIRD AMENDMENT TO LOAN AND SECURITY AGREEMENT AND WAIVER (this
"Amendment"), dated as of July 16, 2003, is entered into by and among WELLS
FARGO FOOTHILL, INC., a California corporation formerly known as Foothill
Capital Corporation, as agent (in such capacity, "Agent") for the Lenders
(defined below), the Lenders signatory hereto, MERCURY AIR GROUP, INC.
("Parent") and Parent's Subsidiaries signatory hereto (together with Parent,
"Borrowers" and each sometimes referred to as a "Borrower").

                                    RECITALS

     A. Borrowers, Agent and the financial institutions from time to time party
thereto (the "Lenders") have previously entered into that certain Loan and
Security Agreement, dated as of December 30, 2002, as amended by that certain
First Amendment to Loan and Security Agreement, dated as of March 12, 2003, and
that certain Second Amendment to Loan and Security Agreement, dated as of March
31, 2003 (as amended, the "Loan Agreement"), pursuant to which the Lenders have
made certain loans and financial accommodations available to the Borrowers.
Capitalized terms used herein without definition shall have the meanings
ascribed thereto in the Loan Agreement.

     B. Borrowers have made or contracted to make Existing Operations Capital
Expenditures of $4,074,324, which amount is in excess of the limit of $4,000,000
set forth in Section 7.19(d)(iii) of the Loan Agreement for such expenditures,
and therefore an Event of Default has occurred (the "Known Existing Default").

     C. Borrowers have requested that Agent and the Lenders waive the Known
Existing Default and amend Section 7.19(d)(iii) to increase the permitted
Existing Operations Capital Expenditures for their fiscal year 2003.

     D. Agent and the Lenders are willing to waive the Known Existing Default
and, along with the Borrowers, amend the Loan Agreement under the terms and
conditions set forth in this Amendment. Borrowers are entering into this
Amendment with the understanding and agreement that, except as specifically
provided herein, none of Agent's or any Lender's rights or remedies as set forth
in the Loan Agreement is being waived or modified by the terms of this
Amendment.

                              AMENDMENT AND WAIVER

     NOW, THEREFORE, in consideration of the foregoing and the mutual covenants
herein contained, and for other good and valuable consideration, the receipt and
sufficiency of which are hereby acknowledged, the parties hereby agree as
follows (initially capitalized terms used herein without definition shall have
the meanings given in the Loan Agreement):

     1. Amendment to Loan Agreement.

<PAGE>

         (a) Section 7.19(d)(iii) of the Loan Agreement is hereby amended by
replacing the amount of "$4,000,000" set forth opposite the fiscal year "2003"
in the table set forth therein to be "$4,400,000."

     2. Waiver of Known Existing Default. Agent and each Lender hereby waives
enforcement of its rights against Borrowers arising from the Known Existing
Default; provided, however, nothing herein shall be deemed a waiver with respect
to any failure of Borrowers to comply fully with Section 7.19(d)(iii) of the
Loan Agreement (as amended by this Amendment). This waiver shall be effective
only for the specific default comprising the Known Existing Default, and in no
event shall this waiver be deemed to be a waiver of enforcement of Agent's or
any Lender's rights with respect to any other Default or Event of Default now
existing or hereafter arising. Nothing contained in this Amendment nor any
communications between any Borrower and either Agent or any Lender shall be a
waiver of any rights or remedies Agent or any Lender has or may have against any
Borrower, except as specifically provided herein. Except as specifically
provided herein, Agent and each Lender hereby reserve and preserve all of their
respective rights and remedies against Borrowers under the Loan Agreement and
the other Loan Documents.

     3. Release; Covenant Not to Sue.


         (a) Each Borrower hereby absolutely and unconditionally releases and
forever discharges Agent and each Lender, and any and all participants, parent
corporations, subsidiary corporations, affiliated corporations, insurers,
indemnitors, successors and assigns thereof, together with all of the present
and former directors, officers, agents and employees of any of the foregoing
(each a "Released Party"), 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 such
Borrower 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 Amendment, whether
such claims, demands and causes of action are matured or unmatured or known or
unknown. It is the intention of each Borrower in providing this release that the
same shall be effective as a bar to each and every claim, demand and cause of
action specified, and in furtherance of this intention it waives and
relinquishes, to the extent permitted by applicable law, all rights and benefits
under any provision of any applicable law that may provide that a general
release does not extend to claims which the person giving the release does not
know or suspect to exist in its favor at the time of executing the release,
which if known by it might have materially affected its settlement with the
recipient of the release. Each Borrower acknowledges that it may hereafter
discover facts different from or in addition to those now known or believed to
be true with respect to such claims, demands, or causes of action and agree that
this instrument shall be and remain effective in all respects notwithstanding
any such differences or additional facts. Each Borrower understands,
acknowledges and agrees that the release set forth above may be pleaded as a
full and complete defense and may be used as a basis for an injunction against
any action, suit or other proceeding which may be instituted, prosecuted or
attempted in breach of the provisions of such release.

         (b) Each Borrower, on behalf of itself and its successors, assigns, and
other legal representatives, hereby absolutely, unconditionally and irrevocably,
covenants and agrees

                                       2
<PAGE>

with and in favor of each Released Party above that it will not sue (at law, in
equity, in any regulatory proceeding or otherwise) any Released Party on the
basis of any claim released, remised and discharged by such Borrower pursuant to
the above release. If any Borrower or any of its successors, assigns or other
legal representations violates the foregoing covenant, such Borrower, for itself
and its successors, assigns and legal representatives, agrees to pay, in
addition to such other damages as any Released Party may sustain as a result of
such violation, all attorneys' fees and costs incurred by such Released Party as
a result of such violation.

     4. Effectiveness of Amendment. Agent must have received the following
before this Amendment is effective:


         (a) this Amendment and the attached Acknowledgement by Guarantors, each
fully executed in a sufficient number of counterparts for distribution to all
parties; and

         (b) a waiver fee in the amount of $25,000, which fee is fully-earned as
of and due and payable on the date hereof.

     5. Representations and Warranties. Each Borrower represents and warrants as
follows:


         (a) Authority. Each Borrower has the requisite corporate power and
authority to execute and deliver this Amendment, and to perform its obligations
hereunder and under the Loan Documents (as amended or modified hereby) to which
it is a party. The execution, delivery and performance by each Borrower of this
Amendment have been duly approved by all necessary corporate action, have
received all necessary governmental approval, if any, and do not contravene any
law or any contractual restrictions binding on each Borrower. No other corporate
proceedings are necessary to consummate such transactions.

         (b) Enforceability. This Amendment has been duly executed and delivered
by the Borrowers. This Amendment and each Financing Agreement (as amended or
modified hereby) is the legal, valid and binding obligation of Borrowers,
enforceable against each Borrower in accordance with its terms, and is in full
force and effect.

         (c) Representations and Warranties. The representations and warranties
contained in each Financing Agreement (other than any such representations or
warranties that, by their terms, are specifically made as of a date other than
the date hereof) are correct on and as of the date hereof as though made on and
as of the date hereof, as modified by any changes to the schedules to the Loan
Agreement reported to the Agent or the Lenders. Parent confirms any changes in
such schedules which are required to be reported to the Agent or the Lenders
under the terms of the Loan Agreement have been reported.

         (d) No Default. After giving effect to the waiver set forth in Section
2 hereof, no event has occurred and is continuing that constitutes an Event of
Default and by entering into this Amendment, except as expressly set forth in
Section 2 hereof, Agent is not waiving and shall not be deemed to have waived
any Event of Default that may exist.

         (e) No Duress. This Amendment has been entered into without force or
duress, of the free will of each Borrower. Each Borrower's decision to enter
into this

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<PAGE>

Amendment is a fully informed decision and such Borrower is aware of all legal
and other ramifications of such decision.

         (f) Counsel. Each Borrower has read and understands this Amendment, has
consulted with and been represented by legal counsel in connection herewith, and
has been advised by its counsel of its rights and obligations hereunder and
thereunder.

     6. Choice of Law. The validity of this Amendment, its construction,
interpretation and enforcement, the rights of the parties hereunder, shall be
determined under, governed by, and construed in accordance with the internal
laws of the State of New York governing contracts only to be performed in that
State.

     7. Counterparts. This Amendment may be executed in any number of
counterparts and by different parties and separate counterparts, each of which
when so executed and delivered, shall be deemed an original, and all of which,
when taken together, shall constitute one and the same instrument. Delivery of
an executed counterpart of a signature page to this Amendment by telefacsimile
shall be effective as delivery of a manually executed counterpart of this
Amendment.

     8. Reference to and Effect on the Loan Documents.


         (a) Upon and after the effectiveness of this Amendment, each reference
in the Loan Agreement to "this Agreement", "hereunder", "hereof" or words of
like import referring to the Loan Agreement, and each reference in the other
Loan Documents to "the Loan Agreement", "thereof" or words of like import
referring to the Loan Agreement, shall mean and be a reference to the Loan
Agreement as modified and amended hereby.

         (b) Except as specifically amended above, the Loan Agreement and all
other Loan Documents, are and shall continue to be in full force and effect and
are hereby in all respects ratified and confirmed and shall constitute the
legal, valid, binding and enforceable obligations of each Borrower to Agent
without defense, offset, claim or contribution.

         (c) The execution, delivery and effectiveness of this Amendment shall
not, except as expressly provided herein, operate as a waiver of any right,
power or remedy of Agent under any of the Loan Documents, nor constitute a
waiver of any provision of any of the Loan Documents.

         (d) To the extent that any terms and conditions in any of the Loan
Documents shall contradict or be in conflict with any terms or conditions of the
Loan Agreement, after giving effect to this Amendment, such terms and conditions
are hereby deemed modified or amended accordingly to reflect the terms and
conditions of the Loan Agreement as modified or amended hereby.

     9. Ratification. Each Borrower hereby restates, ratifies and reaffirms each
and every term and condition set forth in the Loan Agreement, as amended hereby,
and the Loan Documents effective as of the date hereof.

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<PAGE>

     10. Estoppel. To induce Agent and the Lenders to enter into this Amendment
and to continue to make advances to Borrowers under the Loan Agreement, each
Borrower hereby acknowledges and agrees that no right of offset, defense,
counterclaim or objection in favor of any Borrower as against Agent or any
Lender with respect to the Obligations.

     11. Submission of Amendment. The submission of this Amendment to the
parties or their agents or attorneys for review or signature does not constitute
a commitment by Agent or any Lender to waive any of its rights and remedies
under the Loan Documents, and this Amendment shall have no binding force or
effect until all of the conditions to the effectiveness of this Amendment have
been satisfied as set forth herein.

                       [Signatures follow on next page.]



                                       5
<PAGE>


     IN WITNESS WHEREOF, the parties have entered into this Amendment as of
the date first above written.

                            WELLS FARGO FOOTHILL, INC.,
                            a California corporation,
                            as Agent and as a Lender


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


                            ABLECO FINANCE LLC,
                            a Delaware limited liability company,
                            as a Lender


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


                            MERCURY AIR GROUP, INC.,
                            a Delaware corporation


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


                            MERCURY AIR CENTERS, INC.,
                            a California corporation


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


                            MERCURY AIR CARGO, INC.,
                            a California corporation


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



                                       6
<PAGE>


                            MERCFUEL, INC.,
                            a Delaware corporation


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


                            MAYTAG AIRCRAFT CORPORATION,
                            a Colorado corporation


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


                            HERMES AVIATION, INC.,
                            a California corporation


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


                            MERCURY AIR CENTER-BIRMINGHAM, LLC,
                            an Alabama limited liability company


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


                            MERCURY AIR CENTER-BAKERSFIELD, INC.,
                            a California corporation


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


                            MERCURY AIR CENTER-BURBANK, INC.,
                            a California corporation


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

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<PAGE>

                            MERCURY AIR CENTER-FRESNO, INC.,
                            a California corporation


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


                            MERCURY AIR CENTER-LOS ANGELES, INC.,
                            a California corporation


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


                            MERCURY AIR CENTER-ONTARIO, INC.,
                            a California corporation


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


                            MERCURY AIR CENTER-SANTA BARBARA, INC.,
                            a California corporation


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


                            MERCURY AIR CENTER-HARTSFIELD, LLC,
                            a Georgia limited liability company


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



                                       8
<PAGE>


                            MERCURY AIR CENTER-PEACHTREE-
                            DEKALB, LLC,
                            a Georgia limited liability company


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


                            MERCURY AIR CENTER-FT. WAYNE, LLC.,
                            an Indiana limited liability company


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


                            MERCURY AIR CENTER-JACKSON, LLC.,
                            a Mississippi limited liability company


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


                            MERCURY AIR CENTER-RENO, LLC,
                            a Nevada limited liability company


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


                            MERCURY AIR CENTER-TULSA, LLC.,
                            an Oklahoma limited liability company


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


                            MERCURY AIR CENTER-CHARLESTON, LLC.,
                            a South Carolina limited liability company


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


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<PAGE>

                            MERCURY AIR CENTER-JOHNS ISLAND, LLC.,
                            a South Carolina limited liability company

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


                            MERCURY AIR CENTER-NASHVILLE, LLC.,
                            a Delaware limited liability company

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


                            MERCURY AIR CENTER-ADDISON, INC.,
                            a Texas corporation


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


                            MERCURY AIR CENTER-CORPUS
                            CHRISTI, INC.,
                            a Texas corporation


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




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<PAGE>


                         ACKNOWLEDGEMENT BY GUARANTORS

                           Dated as of July __, 2003

     Each of the undersigned, being a Guarantor (each a "Guarantor" and
collectively, the "Guarantors") under their respective Guaranty and Security
Agreement, dated December 30, 2002 and made in favor of Agent for the benefit of
the Lenders (each a "Guaranty" and collectively, the "Guaranties"), hereby
acknowledges and agrees to the foregoing Third Amendment to Loan and Security
Agreement and Waiver (the "Amendment") and confirms and agrees that its Guaranty
is and shall continue to be, in full force and effect and is hereby ratified and
confirmed in all respects except that, upon the effectiveness of, and on and
after the date of the Amendment, each reference in such Guaranty to the Loan
Agreement (as defined in the Amendment), "thereunder", "thereof" or words of
like import referring to the "Loan Agreement", shall mean and be a reference to
the Loan Agreement as amended or modified by the Amendment. Although Lender has
informed Guarantors of the matters set forth above, and Guarantors have
acknowledged the same, each Guarantor understands and agrees that Lender has no
duty under the Loan Agreement, the Guaranties or any other agreement with either
Guarantor to so notify any Guarantor or to seek such an acknowledgement, and
nothing contained herein is intended to or shall create such a duty as to any
advances or transaction hereafter.

     Each Guarantor hereby absolutely and unconditionally releases and forever
discharges each Released Party, 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 such
Guarantor 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 hereof, whether such
claims, demands and causes of action are matured or unmatured or known or
unknown. It is the intention of each Guarantor in providing this release that
the same shall be effective as a bar to each and every claim, demand and cause
of action specified, and in furtherance of this intention it waives and
relinquishes, to the extent permitted by applicable law, all rights and benefits
under any provision of any applicable law that may provide that a general
release does not extend to claims which the person giving the release does not
know or suspect to exist in its favor at the time of executing the release,
which if known by it might have materially affected its settlement with the
recipient of the release. Each Guarantor acknowledges that it may hereafter
discover facts different from or in addition to those now known or believed to
be true with respect to such claims, demands, or causes of action and agree that
this instrument shall be and remain effective in all respects notwithstanding
any such differences or additional facts. Each Guarantor understands,
acknowledges and agrees that the release set forth above may be pleaded as a
full and complete defense and may be used as a basis for an injunction against
any action, suit or other proceeding which may be instituted, prosecuted or
attempted in breach of the provisions of such release. Each Guarantor, on behalf
of itself and its successors, assigns, and other legal representatives, hereby
absolutely, unconditionally and irrevocably, covenants and agrees with and in
favor of each Released Party above that it will not sue (at law, in equity, in
any regulatory proceeding or otherwise) any Released Party on the basis of any
claim released, remised and discharged by such Guarantor pursuant to the above
release. If any Guarantor or any of its successors, assigns or other legal
representations violates the foregoing covenant, such Guarantor, for itself and
its successors, assigns and legal representatives, agrees to pay, in addition to
such other damages as

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<PAGE>

any Released Party may sustain as a result of such violation, all attorneys'
fees and costs incurred by such Released Party as a result of such violation.


                           EXCEL CARGO, INC.,
                           a California corporation


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


                           VULCAN AVIATION, INC.,
                           a California corporation


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


                           MERCURY ACCEPTANCE CORPORATION,
                           a California corporation


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


                           JUPITER AIRLINE AUTOMATION SERVICES, INC.,
                           a Florida corporation


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


                           AEG FINANCE CORPORATION,
                           a Delaware corporation


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


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