* BP evacuating some workers ahead of low-pressure system in US Gulf

* Other oil producers monitoring weather

(Adds details from Mexico's Pemex)

HOUSTON, Oct 2 (Reuters) - A looming low-pressure storm system prompted BP Plc BP.L to evacuate some workers from its four oil and gas platforms in the Gulf of Mexico but production was unaffected, the company said on Wednesday.

Other operators, including Royal Dutch Shell RDSa.L , the biggest oil producer in the Gulf, Anadarko Petroleum Corp

APC.N and Hess Corp HES.N , said they were monitoring the storm but had not begun evacuations.

A Pemex PEMX.UL spokesperson said the company was closely monitoring the forming storm, but it had not ordered any offshore or onshore evacuations at any installations.

The unnamed system had a 70 percent change of becoming a tropical cyclone in the next 48 hours and was expected to cross the northeastern Yucatan Peninsula and move into the southern Gulf by Thursday, according to the U.S. National Hurricane Center. ID:nL4N0HS2SH

About 80 percent of Mexico's oil and gas production comes from mostly shallow-water offshore fields in the potential path of the low pressure system, along the southern rim of the Gulf.

BP, the second-largest oil producer in the Gulf, said workers not essential to production, such as cooks and maids, were being evacuated from its four platforms in the most energy infrastructure-heavy areas of the Gulf.

"With forecasts indicating the disturbance could possibly strengthen into a tropical storm and move across the central Gulf of Mexico, we are now taking additional steps to respond," the company said.

The four platforms have a total capacity of 640,000 barrels per day of oil and 840 million cubic feet per day of natural gas. They include Thunder Horse, the largest oil and gas platform in the world, as well as Atlantis, Na Kika and Mad Dog.

(Reporting by Kristen Hays in Houston, David Alire Garcia in Mexico City, Eileen Houlihan in New York, and Anupam Chatterjee in Bangalore; Editing by Terry Wade, Dan Grebler and Ken Wills)

((kristen.hays@thomsonreuters.com)(+1 713-210-8538)(Reuters Messaging: Reuters Messaging: kristen.hays.reuters.com@reuters.net))

Keywords: GULF STORM/ENERGY