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By Erwin Seba

HOUSTON, Aug 17 (Reuters) - Shell Oil Co <RDSa.L> and Marathon Oil Corp <MRO.N> pulled nonessential workers from the eastern and central Gulf of Mexico due to the threat of Tropical Storm Fay, but offshore production was unaffected, the companies said on Sunday.

Shell said about 200 workers were evacuated on Sunday from the eastern Gulf, the same number the company evacuated from that region on Saturday. Marathon said the number evacuated from the central Gulf was not immediately available.

Both companies described the evacuations as precautionary in the event the storm may bear toward offshore platforms as it progresses into the Gulf, which U.S. forecasters said should take place Monday or Tuesday.

On Sunday, Fay was expected to avoid most of the offshore production areas in the Gulf and instead strike the Gulf Coast of Florida on Tuesday or Wednesday, according to the U.S. National Hurricane Center forecast.

Some computer models, however, predict Fay may enter eastern Gulf production areas before making landfall on the coast of Alabama or Mississippi.

Other companies including the Louisiana Offshore Oil Port LLC, which operates the only U.S. deepwater oil port, said on Sunday they were operating normally while monitoring Fay's progress through the Caribbean Sea toward the Gulf.

The sixth cyclone of what experts predict will be an unusually busy Atlantic hurricane season, Fay may be near hurricane strength as it approaches Cuba on Sunday, and at hurricane strength over the Florida Keys and off Florida's west coast after that, U.S forecasters said.

Fay is the third storm of the 2008 Atlantic hurricane season to menace U.S. offshore oil and natural gas production, which provides 25 percent of U.S. oil output and 15 percent of U.S. natural gas production.

This year's Hurricane Dolly and Tropical Storm Edouard only temporarily shut fractions of offshore production and did not outweigh geopolitical factors or the U.S. economic outlook in determining crude oil and refined products prices.

Gulf of Mexico producers fear a repeat of 2005 when Hurricanes Katrina and Rita temporarily shut a quarter of U.S. oil and fuel production, sending prices to then-record highs.

As of 5 p.m. EDT (2200 GMT) Fay was off Cuba's southern coast, according to the National Hurricane Center.

Shell Oil Co, the U.S. unit of Royal Dutch Shell Plc, is the leading deepwater producer in the Gulf of Mexico, from where it draws 80 percent of its U.S. oil and natural gas production, according to the company's website.

Among Shell's eastern-most Gulf platform is the Ram-Powell. Other eastern Gulf Shell platforms Mars and Ursa. (Editing by Richard Chang)

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