None of Chevron's offshore production has been shut in due to Dorian, the company said. BHP said it does not expect an impact to its operations.

Exxon Mobil Corp and Occidental Petroleum said they are closely monitoring Dorian, and Gulf of Mexico operations were operating normally.

Other oil companies with operations in the US-regulated north Gulf of Mexico did not reply to requests for comment about offshore operations.

Chevron said its Pascagoula, Mississippi refinery continues to monitor the storm.

Shell Oil Co, the US arm of Royal Dutch Shell Plc , has not modified operations at its Norco and Convent, Louisiana, refineries, according to spokesman Ray Fisher. Shell spokeswoman Cynthia Babski said offshore operations were not affected by the storm's threat.

Offshore platforms account for 16 percent of US crude oil production. Evacuations were set for Chevron's Petronius and Blind Faith and BHP's Neptune and Shenzi platforms, the companies said.

Dorian is forecast to strike the Atlantic coast of Florida by early next week as a major hurricane. Some computer models project Dorian may cross the Florida peninsula and enter the Gulf of Mexico.