U.S. gasoline supplies have amassed a nine percent surplus over last year, bringing them to the highest level since 1999 as extraordinary amounts of imports arrived to the nation's shores last month, the U.S. government said on Wednesday.

"Our imports of gasoline averaged close to 1.0 million barrels per day in the last four weeks, which is very high for February," said Doug MacIntyre, an analyst for the Energy Information Administration (search), the statistical arm of the Department of Energy (search).

"Why are we continuing to import so much fuel with such high stockpiles? I don't know," he said.

The swelling stockpile has eased the market's concerns of a spring supply crunch in the United States, the world's largest energy consumer. But it has done little to cool red-hot prices.

"Demand growth has become so strong that these higher supply levels don't represent the same daily demand coverage they used to," said MacIntyre. "SUVs are making up a bigger percentage of the fleet and the average American tends to drive more miles."

SUVs consume more gas per mile than many cars.

Gasoline demand is expected to average 9.22 million barrels per day this year, compared to 8.4 million bpd in 1999, MacIntyre said.

NYMEX gasoline futures (search) rose 4.13 cents to $1.4440 a gallon after the EIA released its weekly supply data. The report also showed an increase in crude supply and a drop in distillate stockpiles.