With the approach of Tropical Storm Isaac in the Gulf of Mexico, about 24.2 percent of the gulf's daily oil production and about 8.2 percent of its daily natural-gas production has been shut-in, according to estimates of the U.S. Interior Department's Bureau of Safety and Environmental Enforcement, or BSEE.

This represents about 333,815 barrels of oil per day and about 371 million cubic feet of natural gas per day.

Oil-and-gas operators in the gulf have evacuated at least 39 production platforms -- equivalent to 6.5 percent of the 596 manned platforms there -- the BSEE reported.

O&G operators also have evacuated at least eight drilling rigs -- equivalent to 10.5 percent of the 76 rigs operating at present in the gulf -- the BSEE said.

These BSEE figures are based on numbers submitted to it by O&G operators as of Sunday at 12:30 p.m. EDT.

Based on both Tropical Storm Isaac's anticipated path and the O&G industry's history of operations in similar situations, significantly more output most likely will be shut-in during the next couple of days.

Accordingly, light sweet crude oil prices were moving higher by more than 1 percent in CME Group Globex futures trading on Sunday night.

Meanwhile, the U.S. National Hurricane Center's latest advisory on Isaac puts the eye of the storm about 530 miles southeast of the mouth of the Mississippi River, with the system moving west-northwest at 15 mph. The maximum sustained winds are 65 mph, and the minimum central pressure is 29.26 inches.

"Some strengthening is forecast during the next 48 hours," the NHC reported on Sunday at 8 p.m. EDT, "and Isaac is expected to become a hurricane in a day or two."