Nearly 30% of US Gulf of Mexico oil output offline after storm

(Adds cumulative loss estimate from Hurricane Francine in paragraph 4)

HOUSTON, Sept 14 (Reuters) - Nearly 30% of U.S. Gulf of Mexico crude oil production and 41% of its natural gas production remained offline on Saturday following Hurricane Francine, the U.S. offshore energy regulator said.

Francine churned through prime oil and gas producing areas in the U.S. Gulf of Mexico and slammed into Louisiana with up to 100 miles per hour (161 kph) winds. The midweek storm toppled trees, flooded coastal areas and knocked out power across four states. There were some 37,000 customers in Louisiana without power on Saturday.

A survey of energy producers showed more than 522,000 barrels of oil production and 755 million cubic feet of natural gas remained offline on Saturday, the Bureau of Safety and Environmental Enforcement said.

Cumulative offshore production losses this week due to Francine total 1.82 million barrels of crude oil and 4.12 billion cubic feet of natural gas, according to BSEE estimates.

There were 52 oil and gas platforms unmanned by energy workers on Saturday, about 14% of the total, down from 171 evacuated offshore platforms at peak earlier in the week, the offshore regulator said.

Two of Chevron's platforms were operating at reduced rates due to an onshore gas plant disruption, the company said on Saturday. Full production at the two - Jack/St. Malo and Big Foot - will resume after the onshore disruption is resolved, it said.

Chevron did not identify the operator of the gas plant.

The second-largest U.S. oil producer said it was continuing to return workers and restore oil production at its Anchor and Tahiti platforms that were shut-in ahead of hurricane Francine. Initial assessments show neither suffered significant damages, Chevron said. (Reporting by Gary McWilliams; Editing by Alistair Bell and Diane Craft)