The US government says oil and gas operators are evacuating offshore platforms and rigs that could wind up in Tropical Storm Isaac's path through the Gulf of Mexico.
Isaac is expected to become a Category 2 hurricane before making landfall late on Tuesday or early Wednesday.
The bureau of Safety and Environmental Enforcement says 39 production platforms and eight drilling rigs have been evacuated as of Sunday.
That's about 6.5 per cent of the 596 manned platforms and 10.5 per cent of the 76 rigs operating in the Gulf of Mexico.
Evacuation procedures include closing safety valves under the ocean floor to avoid pollution in case a rig or platform is damaged.
The bureau says operators estimate that about 24 per cent of the current daily oil production and eight per cent of natural gas production has been cut off.