<PAGE>   1
                                                                  EXHIBIT 10(aa)

PORTIONS OF THIS EXHIBIT IDENTIFIED BY "***" HAVE BEEN DELETED PURSUANT TO A
REQUEST FOR CONFIDENTIAL TREATMENT FILED WITH THE SECURITIES AND EXCHANGE
COMMISSION UNDER RULE 24b-2 OF THE SECURITIES EXCHANGE ACT OF 1934, AS AMENDED,
AND THE FREEDOM OF INFORMATION ACT.

                         MOBILE GAS SERVICE CORPORATION
                            TRANSPORTATION AGREEMENT

     THIS AGREEMENT is made and entered into as of this 26th day of September,
1997 by and between MOBILE GAS SERVICE CORPORATION, an Alabama corporation,
with a mailing address of P. O. Box 2248, Mobile, Alabama 36652, herein called
"Mobile Gas," and METHANOL ONE of ALABAMA, L.L.C., an Alabama limited liability
corporation, with a mailing address of P. O. Box 1234, Slidell, Louisiana
70459, herein called "Customer."

     Whereas, Customer desires to use natural gas for the operation of
Customer's proposed chemical manufacturing facility to be located in Theodore,
Alabama (the "Plant"); and

     Whereas, Mobile Gas operates a system for the distribution of natural gas
from natural gas transmission pipelines and processing plants and Customer
intends that it or its agents will purchase natural gas from third parties
("Customer's Shippers") who will deliver such gas to Mobile Gas for redelivery
to the Plant.

     NOW THEREFORE, in consideration of the mutual covenants herein contained,
the parties hereto agree as follows:

                       ARTICLE I - TRANSPORTATION SERVICE

1.1  Mobile Gas will transport up to the "Contract Demand Volume," which shall
be *** MMBtu per day, of Customer's gas, not to exceed *** MMBtu per hour.
Customer will pay Mobile Gas for all gas transported by Mobile Gas to the Plant
and agrees to accept and pay for service subject to the terms and conditions
hereof:

1.2  The RATE for such transportation service and the *** hereunder are as
specified in Exhibit "A" which is attached hereto and made part of this
agreement. The rate is a special negotiated rate.

1.3  Customer may request that the Contract Demand Volume be increased by
delivering a written request to Mobile Gas for such increase.  Mobile Gas may
approve or decline such request in its discretion (such request being deemed to
be declined if Mobile Gas does not approve the request within 30 (thirty) days
after the date of receipt thereof).  In the event Mobile Gas approves such a
request, it may specify an effective date for the requested increase in the
Contract Demand Volume, such date to be not later than 24 months after the
approval date.

1.4  Except as otherwise specified in this section, Mobile Gas shall be the ***
of natural gas to Customer during the term of this Agreement.  If during the
term of this Agreement Mobile Gas, due to default by Mobile Gas or force
majeure affecting Mobile Gas is unable to deliver adequate volumes, Customer
may obtain gas volumes from other sources for the duration of such default or
force majeure.  If during
<PAGE>   2
the term of this Agreement Customer's operations require an increase in the
Contract Demand Volume, and such increase is requested by Customer and not
approved by Mobile Gas as described in Section 1.3, Customer may obtain
transportation of gas volumes exceeding the Contract Demand Volume from other
sources.

                         ARTICLE II - TERM OF AGREEMENT

2.1  The term of this Agreement shall be *** years, beginning on the
Commencement Date, as herein defined, and shall be automatically extended for a
period of two years from each expiration date of such term or any automatic
extension thereof unless either party shall notify the other in writing not
less than 90 days prior to the expiration date, or the expiration of any two
year extension of such expiration date, of its intention to terminate this
Agreement.

2.2  The "Commencement Date" shall be the earlier of (i) the first day of the
month following the date ninety (90) days after written notification by
Customer of intended plant completion (ii) the date Customer first takes
redelivery of natural gas from Mobile Gas at the Point of Redelivery, or (iii)
December 31, 1999.  In no case shall the Commencement Date be before April 1,
1999.

2.3  Notwithstanding the provisions of Section 2.1, this Agreement shall become
effective as of the date hereof with respect to the obligations of the parties
specified in Section 4.4 hereof, and payment obligations arising prior to
expiration or termination of this Agreement shall remain in effect after the
term of this Agreement.

2.4  This Agreement may only be terminated prior to the expiration of the
initial term or a renewal term hereof, if any, as the case may be:

(a)  by Mobile Gas, (i) in accordance with Section 5.3, or (ii) after
occurrence of any other material breach by Customer in the performance of its
obligations hereunder and the continuance of such breach 30 days after written
notice by Mobile Gas to Customer of such breach and demand by Mobile Gas that
Customer cure same.

(b)  by Customer after occurrence of any material breach by Mobile Gas in the
performance of its obligations hereunder and the continuance of such breach 30
days after written notice by Customer to Mobile Gas of such breach and demand
by Customer that Mobile Gas cure same.  In the event of termination by either
party under this Section 2.4 Customer shall not owe any minimum bill payments
as provided for in Exhibit A beyond the date of termination.
<PAGE>   3
                             ARTICLE III - QUALITY

3.1  The volumes of natural gas delivered hereunder shall be measured at an
equivalent pressure base of 14.73 pounds per square inch absolute (psia) and an
assumed atmospheric pressure of 14.7 psia, and at a temperature base of 60
degrees Fahrenheit.  The volume of natural gas determined hereunder may be
adjusted to give effect to Boyle's Law in accordance with standard procedure.

3.2  The quality of the gas delivered by Customer's Shippers to Mobile Gas
shall be pipeline quality, and:

(a)  Shall be dehydrated and shall in no event have a water content in excess
of seven (7) pounds of water per million (1,000,000) cubic feet of gas measured
at a pressure base of 14.73 psi and at a temperature base of 60 degrees
Fahrenheit, as determined by dew point or other moisture measuring equipment in
general use in the industry.

(b)  Shall not contain more than one (1) grain of hydrogen sulfide per one
hundred (100) cubic feet as determined by quantitative methods in general use
in the industry.

(c)  Shall not contain more than twenty (20) grains of total sulphur, including
hydrogen sulfide, per one hundred (100) cubic feet as determined by
quantitative methods in general use in the industry.

(d)  Shall not contain in excess of:

     (i) Three percent (3.0%) by volume carbon dioxide.

     (ii)  Two tenths percent (0.2%) by volume oxygen.

(e)  Shall be commercially free from dust, gum, gum-forming constituents or
other liquid or solid matter which might become separate from the gas in the
course of transportation through pipelines.

(f)  Shall be commercially free of water and other objectionable liquids at the
temperature and pressure at which the gas is delivered and the gas shall not
contain any hydrocarbons which might condense to free liquids in the pipeline
under normal pipeline conditions.
<PAGE>   4
                 ARTICLE IV - POINT OF DELIVERY AND REDELIVERY

4.1  The Point of Delivery by Customer's Shippers to Mobile Gas shall be as
specified in Exhibit A, Customer's Shippers shall make delivery to the Point of
Delivery at a minimum pressure sufficient to enable Mobile Gas to redeliver gas
to Customer at a minimum of 400 pounds per square inch gauge.  Mobile Gas shall
not be obligated to redeliver gas at the Point of Redelivery unless Customer's
Shippers make delivery at the Point of Delivery as specified in this Section
4.1.

4.2  The Point of Redelivery of natural gas hereunder to Customer shall be the
Customer's flange downstream of the Mobile Gas metering station to be located
on Customer's Plant premises.  Maintenance by Mobile Gas of gas pressure of a
minimum of 400 pounds per square inch gauge at the Point of Redelivery shall
constitute redelivery of gas for purpose of this Agreement.

4.3  The gas shall be redelivered by Mobile Gas to Customer in like good order
and condition and at quality in accordance with specifications as set forth in
Article III of this agreement.

4.4  Customer shall be responsible for construction of its pipeline from the
Point of Redelivery to its Plant.  Mobile Gas shall at its expense construct
such facilities as may be necessary to enable it to redeliver gas to Customer
at the Point of Redelivery at the Contract Demand Volume on the Commencement
Date.  Customer shall provide to Mobile Gas such easement or easements, in form
reasonably acceptable to Mobile Gas, covering approximately 100 feet by 100
feet of Customer's property, for construction of pipelines, for above and below
ground facilities to the Point of Redelivery as shall cross property owned or
leased by Customer, as well as for maintenance of a metering station on
Customer's premises.

                              ARTICLE V - BILLING

5.1  On or before the seventh (7th) working day of each calendar month, Mobile
Gas shall render to Customer, a statement of the amount of gas transported
hereunder by Mobile Gas to Customer during the preceding, calendar  month (and
with respect to the first such statement, with respect to the portion of a
month, if any, between the Commencement Date and the first full calendar
month), and shall also render a bill for all gas so transported.  On or before
the twenty-first (21st) day of each calendar month, Customer shall make payment
to Mobile Gas at Mobile Gas' office, P. O. Box 2248, Mobile, Alabama 36652.

5.2  In the event that Customer disputes any amount shown on a statement issued
by Mobile Gas to Customer, such disputed amount shall be paid.  Notwithstanding
such payment, Customer shall have the right to claim from Mobile Gas such
disputed amount.  Upon receipt by Mobile Gas of any claim from Customer for a
disputed amount, Mobile Gas and Customer shall endeavor to amicably resolve the
disputed amount prior to institution of arbitration by Customer.  The parties
are not obligated to pursue amicable resolution for more than ten (10) days.
<PAGE>   5
5.3  Should Customer fail to pay any amount due (except for any minimum
billings as specified in Exhibit A falling due during any period of force
majeure invoked by Mobile Gas pursuant to Section 6.1) to Mobile Gas when the
same is due, Mobile Gas shall give notice and interest shall accrue on all
unpaid amounts from the date due until paid at a rate of interest equal to 2%
in excess of the "prime rate" reported in the Wall Street Journal or any
successor thereto.  Should such failure to pay continue for ten (10) days,
Mobile Gas may suspend deliveries of gas hereunder, and the exercise of such
right shall be in addition to any and all remedies available to Mobile Gas.
Should such failure to pay continue for ninety (90) days after written notice
is given by Mobile Gas to Customer of such failure to pay, Mobile Gas may
terminate this Agreement, and the exercise of such right shall be in addition
to any and all remedies available to Mobile Gas.  Such termination shall not
relieve Customer of its payment obligations hereunder.

                           ARTICLE VI - FORCE MAJEURE

6.1 In the event Mobile Gas is rendered unable, wholly or in part, by reason of
force majeure to carry out its obligations under this Agreement, it is agreed
that Mobile Gas shall give notice and reasonably full particulars of such force
majeure, in writing by either mail, hand delivery, or facsimile, to Customer
within a reasonable time after the occurrence of the cause relied on, and the
obligations of Mobile Gas, so far as they are affected by such force majeure,
shall be suspended during the continuance of any inability so caused, but for
no longer period, and such cause shall, so far as possible, be remedied with
all reasonable dispatch.

6.2 In the event the Customer is rendered unable, wholly or in part, by reason
of force majeure to carry out its obligations under this Agreement (other than
the obligation to make payment of amounts due hereunder), which obligations
shall not be affected by events of force majeure), it is agreed that Customer
shall give notice and reasonably full particulars of such force majeure, in
writing by either mail, hand delivery, or facsimile, to Mobile Gas within a
reasonable time after the occurrence of the cause relied on, and the
obligations of Customer, so far as they are affected by such force majeure,
shall be suspended during the continuance of any inability so caused, but for
no longer period, and such cause shall, so far as possible, be remedied with
all reasonable dispatch.

6.3 The term, "force majeure," as employed herein shall mean acts of God;
strikes, lockouts, or other industrial disturbances; conditions arising from a
change in governmental laws, orders, rules or regulations; acts of public
enemy; wars; blockades; insurrections; riots; epidemics; landslides; lightning;
earthquakes; fires; storms; floods; washouts; arrests and restraints of
governments and people; civil disturbances; explosions; breakage or accident to
machinery or lines of pipe; the necessity for making repairs, tests or
alterations to machinery or lines of pipe; freezing of wells or lines of pipe;
partial or entire failure of wells, processing or gasification and gas
manufacturing facilities; and any other causes, whether of the kind herein
enumerated or otherwise, not within the control of the party claiming
suspension, and which by the exercise of due diligence, such party is unable to
prevent or overcome.  Such term shall likewise include:  (a) those instances
where either Mobile Gas or Customer is required to obtain servitudes,
rights-of-way, grants, permits or licenses to enable such party to fulfill its
<PAGE>   6
obligations under this Agreement; such party is unable to acquire, at
reasonable costs, and after the exercise of reasonable diligence, such
servitudes, rights-of-way, grants, permits or licenses, and (b) those instances
where either Mobile Gas or Customer's Shipper or Customer  is required to
furnish materials and supplies for the purpose of constructing or maintaining
facilities or is required to secure permits or permissions from any
governmental agency to enable such party to fulfill its obligations under this
Agreement and such party is unable to acquire, or is delayed in acquiring, at
reasonable costs, and after the exercise of reasonable diligence, such
materials and supplies, permits and permissions.  Force majeure shall not
include failure of gas supply due to pricing considerations.

6.4  It is understood and agreed that the settlement of strikes or lockouts
shall be entirely within the discretion of the party having the difficulty, and
that the above requirement that any force majeure shall be remedied with all
reasonable dispatch shall not require the settlement of strikes or lockouts by
acceding to the demands of the opposing party when such course is inadvisable
in the discretion of the party having the difficulty.

                           ARTICLE VII -  ARBITRATION

7.1  Any controversy or claim arising out of or relating to this Agreement, or
the breach thereof, shall be settled exclusively by arbitration pursuant to the
Commercial Arbitration Rules of the American Arbitration Association.

7.2  All arbitrations pursuant to this Agreement shall be held at Mobile,
Alabama.

There shall be three arbitrators.  One of the arbitrators shall be appointed by
Mobile Gas, the second by Customer, and the third shall be a neutral arbitrator
selected by these two arbitrators.  Such neutral arbitrator shall be chairman
of the arbitration panel.

The arbitration shall be decided by a majority vote of the arbitration panel.
The cost of arbitration, including the fees of the arbitrators, shall be borne
by the losing party, unless the arbitrators decide otherwise.

                       ARTICLE   VIII- SPECIAL PROVISIONS

     The following Special Provisions for TRANSPORTATION are made a part
hereof:

8.1       If, on any day, Customer takes unauthorized volumes of gas, Customer
shall pay to Mobile Gas, as damages, any gas costs incurred by Mobile Gas.  The
payment of damages for unauthorized volumes by Customer shall not under any
circumstances, be considered as giving Customer the right to take unauthorized
volumes, nor shall such payment be considered as a substitute for any other
remedies available to Mobile Gas against Customer for failure to respect its
obligations to adhere to the provisions of its contract with Mobile Gas.
<PAGE>   7
8.2       In the event, Mobile Gas incurs any cost, expense and/or penalties
resulting from Customer being over or under nominated for any period of time,
the Customer shall reimburse Mobile Gas for such cost, expenses and/or
penalties.  Nomination shall be made using existing practices and procedures
subject to change in accordance with industry standards.

8.3       A "day" when used in this Agreement shall mean a twenty-four (24)
hour period ending at 9:00 A.M. Mobile, Alabama Time.

8.4       (a)   Gas delivered will be measured through one or more meters,
either turbine meters, orifice meters, or combination of the two, each
installed and maintained by Mobile Gas.  Mobile Gas will inspect such meters
from time to time, and shall keep measuring equipment accurate and in repair.
Inspection shall be in accord with A.G.A. Report 3 for orifice meters or A.G.A.
Report 7 for turbine meters, as may be amended from time to time.  Mobile Gas
shall give  Customer reasonable notice on the day preceding tests conducted on
measuring equipment in order that, if Customer desires, Customer may have its
representative present.

          (b)   Upon written request of Customer, Customer may challenge the
accuracy of measuring equipment and, when challenged, the equipment shall be
tested, calibrated, and, if necessary, repaired by Mobile Gas.  Customer shall
bear the cost of such special tests if the measuring equipment is found to be
accurate to the extent that it affects the measuring accuracy by an amount of
two percent (2%) or less.

          (c)   Customer may, at its option and expense, install and operate a
check meter to check Mobile Gas' meter, but measurement of gas delivered to
Customer, for the purpose of this Agreement shall be by Mobile Gas' operated
metering only.  Any check meter installed shall be of standard type and shall
be subject at all reasonable times to inspection or examination by Mobile Gas,
but the reading, calibration and adjustment thereof and changing of charts
shall be done only by the employees or agents of Customer.

          (d)  Mobile Gas shall provide Customer appropriate signals from its
measuring equipment that shall enable the Customer to calculate daily an
accumulated flow.

8.5       (a)   Mobile Gas agrees to protect, defend, indemnify, and hold
harmless the Customer, its officers, directors, agents, contractors and/or
employees from and against any claims, demands, losses, damages, suits and
expenses, for damages and/or injury to persons and/or property which may be
brought against Customer, its officers, directors, agents, contractors and/or
employees arising out of, or resulting from, the transportation of natural gas
from the Point of Delivery to the Point of Redelivery pursuant to the terms and
conditions expressed herein.

          (b)   Customer agrees to protect, defend, indemnify, and hold
harmless Mobile Gas, its officers, directors, agents, contractors, and/or
employees from and against any claims, demands, losses, damages, suits and
expenses, for damages and/or injury to persons and/or property which may be
brought against Mobile Gas, its
<PAGE>   8
officers, directors, agents, contractors and/or employees arising out of, or
resulting from, the transportation of natural gas by Customer or its agents or
contractors to the Point of Delivery and from the Point of delivery to and
through its Plant and facilities.

8.6  (a)  Customer warrants for itself, its successors and assigns, that it
will have at the time of delivery of gas for transportation hereunder good
title or valid right to deliver such gas hereunder; that the gas it delivers
hereunder shall be free and clear of all liens, encumbrances, or claims
whatsoever; and that it will indemnify Mobile Gas and save it harmless from all
claims, suits, actions, damages, costs and expenses arising directly or
indirectly from or with respect to the title to gas tendered to Mobile Gas
hereunder.

     (b)  As between Customer and Mobile Gas, Customer shall be in control and
possession of the gas transported hereunder prior to delivery to Mobile Gas at
the Point of Delivery and after delivery by Mobile Gas to Customer at the Point
of Redelivery, and Mobile Gas shall be in control and possession of the gas
after the receipt of the same at the Point of Delivery and until delivery by
Mobile Gas to Customer at the Point of Redelivery.  The risk of loss for all
gas transported hereunder shall be and remain with the party having control and
possession of the gas as herein provided.

8.7  Mobile Gas shall use due diligence to provide continual service and having
used reasonable diligence shall not be liable to Customer for failure or
interruption of service.

8.8  The authorized agents of Mobile Gas shall have, at all times, the right of
access to the Plant premises for the purpose of examining and inspecting such
meters and/or for other necessary purposes.

8.9     So long as all amounts due and payable to Mobile Gas at such time have
been paid by customer, Mobile Gas agrees to transport additional volumes of gas
to Customer for a period of up to ten (10) days beyond the termination of this
Agreement in order to bring into balance any imbalance that exists at the
termination of this Agreement.

8.10 This Agreement shall not be assigned or transferred by either party
without prior written consent of the other party, which consent shall not be
unreasonably withheld.  Subject to the foregoing, this Agreement shall be
binding upon and inure to the benefit of the respective  legal representatives,
successors and assigns of the parties hereto.

8.11 In the event one or more of the provisions contained herein shall for any
reasons be held to be invalid, illegal, or unenforceable in any respect, such
invalidity, illegality, or unenforceability shall not affect any other
provision hereof and this Agreement shall be construed as if such invalid,
illegal, or unenforceable provision had never been contained herein.

8.12 This Agreement is contingent upon approval by the Alabama Public Service
Commission.
<PAGE>   9
     IN WITNESS WHEREOF, each party hereto has caused this Agreement to be
executed by its officer thereunto dully authorized as of the date first above
written.

WITNESS:                                MOBILE GAS SERVICE CORPORATION



/s/ G. Edgar Downing, Jr.               By: /s/ W. G. Coffeen III         
-------------------------                  -------------------------------
                                        Its: Vice President Marketing     
                                            ------------------------------




WITNESS:                                METHANOL ONE OF ALABAMA, INC.




 /s/ Michael James                      By: /s/ Dane E. Revette          
------------------------                   ------------------------------
                                        Its: Vice President               
                                           ------------------------------
<PAGE>   10
                                  EXHIBIT "A"
                         MOBILE GAS SERVICE CORPORATION
                       TRANSPORTATION SERVICE CONDITIONS

     TRANSPORTATION SERVICE CONDITIONS


     1.   Special Monthly Transportation Rate "A"


<TABLE>
<CAPTION>
          MMBtu per month                                     RATE     
          ------------------------                    -----------------

          <S>                                         <C>
          If less than ***                            ***

          If over ***

          First ***                                   *** per MMBtu for all MMBtu 
                                                      transported during the
                                                      month

          Over ***                                    *** per MMBtu for all
                                                      MMBtu above *** MMBtu.
</TABLE>

         2.      ***

                 The *** monthly bill for such transportation will be *** per 
                 MMBtu of Contract Demand Volume.

         3.      Rate Adjustment

                 The rates and minimum bill shall be adjusted by the annual per
                 centage upward or downward) in the "PPI" on the anniversary 
                 date and year-to-year thereafter for as long as this agreement
                 shall remain in full force and effect.

                 In no year shall the annual percentage change in the "PPI" be
                 taken to be greater than *** upward or downward.

                 The term "PPI" means the Producer Price Index (PPI) as 
                 published by the U. S. Department of Labor, Bureau of Labor 
                 Statistics.

         4.      Point of Delivery

                 The Point of Delivery shall be the Shell Processing Plant 
                 interconnect or Mobil Processing Plant interconnect near 
                 Coden, Alabama, or other mutually agreeable interconnect on 
                 the Mobile Gas Bellingrath Pipeline.