Oct. 15 (Bloomberg) -- Exxon Mobil Corp., the world's largest oil company, plans to shut a gasoline-making unit at the smaller of its two French refineries for repairs early next year, an official with knowledge of the work said.

A so-called fluid catalytic cracker at the Fos plant on France's south coast will close in January for a month, the official said, declining to be identified because he isn't allowed to speak publicly about the work. Associated units will also be taken off line, he said.

Exxon's spokeswoman in Paris, Sylvie Sanders, said she isn't authorized to comment on plant shutdowns.

The FCC unit can handle 28,000 barrels of oil a day, about a quarter of the refinery's 119,000-barrel-a-day processing capacity, according to data compiled by Bloomberg. FCCs process vacuum gasoil into higher-value gasoline or lighter crude products.

Gasoline for immediate loading in Amsterdam-Rotterdam- Antwerp, Europe's trading hub, soared to an all-time high of $1,192 a metric ton in July after refinery maintenance curtailed output and record oil prices boosted fuel production costs. Spot gasoline has since declined to $663 a ton, Bloomberg data show.

Exxon has a 233,000-barrel-a-day refinery at Gravenchon in Normandy, northern France, according to the company's Web site. The two plants combined account for 20 percent of the country's fuel needs.

Gravenchon Closure

The Irving, Texas-based company will shut units including a 34,000-barrel-a-day FCC at Gravenchon in the first quarter of next year, an official said in January.

Refining margins, or the profit from turning a barrel of oil into fuels such as gasoline and diesel, have almost doubled in northwestern Europe, rising to $8.04 a barrel in September from $4.13 a barrel in August, the Organization of Petroleum Exporting Countries said in a report today.

Refiners along the U.S. Gulf Coast earned as much as $22.90 a barrel last month, compared with $6.16 in August, as they restarted plants that had shut before hurricanes Gustav and Ike swept through the region, according to the report.

To contact the reporter on this story: Nidaa Bakhsh in London at nbakhsh@bloomberg.net

Last Updated: October 15, 2008 12:13 EDT