Exhibit 10(s)

Exhibit 10(s)

[BP Letterhead]

September 8, 2003

PCS Nitrogen Ohio, L.P.

Dear Don:

This letter amends the Manufacturing Support Agreement (“Support Agreement”) and the Operating Agreement (“Operating Agreement”) both between BP Chemicals Inc. (“BP”) and PCS Nitrogen Ohio, L.P., formerly Arcadian Ohio, L.P., (“PCS”), dated May 11, 1993 and each as previously amended. BP understands that both parties desire to modify the cost of Steam set forth in those Agreements, including the Boiler Feed Water component of the cost of Steam. Consequently, BP proposes that the two Agreements be modified, retroactive back to January 1, 2003, as follows:

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All other terms and conditions of the Support Agreement and the Operating Agreement would remain the same.

If you are in agreement, please have an authorized representative sign below and return one fully executed original to BP.

BP CHEMICALS INC.

ACCEPTED AND AGREED:

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“EXHIBIT D, 2003 STEAM”

Addendum to the BP/PCS Operating Agreement for Calculating BP Export Steam

Items for PCS to Enter:

Estimated PCS BFW Cost 18.4079 $/MGAL

PCS/BP Steam Transfers

PCS Steam Usages

PCS/BP BFW Transfers

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Outputs

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Addendum to the BP/PCS Operating Agreement for Calculating BP Export Steam Price to PCS & PCS BFW Price to BP

Heat Required to Make AOGI Steam

BFW Make-up from PCS Demin Plant to AOGI Economizer

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Formulas

Cost to Make AOGI Steam (based on Nat Gas Fuel Value):

SH Stm Natural Gas Cost = [Natural Gas Cost $/MMBtu] x [BTU rqmt for AOGI steam from above = B17] x [1000 lb/Mlb] / [1000000 Btu/MMBtu]

BFW from PCS Cost = [PCS BFW Cost $/Mgal] x [12% blowdown adjustment = 1.12] / [Density of water = 8.34 lb/gal]

Cost to Make Reactor Steam (based on Nat Gas Fuel Value):

Sat Stm Natural Gas Cost = [Natural Gas Cost $/MMBtu] x [BTU rqmt for Rxtr steam from above = B25] x [1000 lb/Mlb] / [1000000 Btu/MMBtu]

City Water to Zeolites Cost = [City Water Cost $/Mgal] x [15% softener regen blowdown adjustment = 1.15] / [Density of water = 8.34 lb/gal]

50# Stm to DA = [Refinery 50# Steam Cost $/Mlb] x [50# Steam Required to Dearate 1 lb of BFW used to Make Reactor Steam = 0.0385 lb]

Chemicals Cost = [Typical Yearly Cost of Chemicals to Treat BFW and Reactor Steam $] / [Typical Yearly Production of Reactor Steam Mlb]

Electricity Cost = [Electricity Cost $/kWH] x [Total Horsepower of the three pumps = 750 hp] / [Horsepower to Watt conversion = 0.00134 hp/W] x [1000 W/Kw] x [Average Reactor Steam Production = 281 Mlb/hr]

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Addendum to the BP/PCS Operating Agreement for Calculating BP Export Steam

      “The D” term is the calculated PCS BFW to BP Price determined through an Iterative Calculation to remove the spiraling effect of any increases or decreases to any variable used in both the Steam and BFW price calculations. An example of this calculation is set forth on this page. “BFW Cost ($/Mgal) column will be the “D” term used in the calculation set forth on page 1 of this Exhibit”

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