Forecasters said Gustav might slip between Mexico's Yucatan Peninsula and the western tip of Cuba on Sunday, then march toward a Tuesday collision with the U.S. Gulf Coast — anywhere from south Texas to the Florida panhandle.

"We know it's going to head into the Gulf. After that, we're not sure," said meteorologist Rebecca Waddington at the National Hurricane Center. "For that reason, everyone in the Gulf needs to be monitoring the storm."

Gustav is the first storm of the 2008 Atlantic hurricane season to pose a serious threat to the more than 4,000 oil and gas installations in the Gulf. In 2005, Katrina and Rita destroyed 109 oil platforms and five drilling rigs.

Oil prices were also supported by a weaker dollar, which boosted the demand for oil among investors who buy commodities as a hedge against inflation. The euro gained to $1.4767 while the dollar fell to 109.39 yen.

In other Nymex trading, heating oil futures rose 4.48 cents to $3.3065 a gallon, while gasoline prices gained 4.28 cents to $3.11 a gallon. Natural gas futures added 5.7 cents to $8.665 per 1,000 cubic feet.