But government and industry officials say refiners have enough oil, and that if war in Iraq should disrupt the supply, the United States and other industrial countries are ready to draw on government reserves.
While inventories are low, "it doesn't necessarily mean there will be shortages. ... Refineries are still running," said Ron Planting, an economist for the American Petroleum Institute, the trade group of the major oil companies.
Still, the low inventories could hamper the smooth flow of gasoline and heating oil from refineries. Stocks of heating oil are one-third below comfortable levels and gasoline inventories - though up last week - remain lower than they should be, according to the government.
Demand for both has been higher than expected.
The Energy Department said Wednesday that crude stocks fell by 4.5 million barrels last week to 269.8 million barrels, just below the minimum to assure efficient refinery operation. That is the lowest level since October 1975, when refiners used about 20 percent less oil than today.
The continued decline of crude stocks, as the Bush administration makes war preparations, was expected to prompt renewed calls for drawing on some of the 600 million barrels of oil in the government's emergency Strategic Petroleum Reserve.
President Bush has resisted several such calls in recent weeks.
Energy Secretary Spencer Abraham said his department continues to monitor the oil inventory situation. "We have not changed our view" that those reserves should be used, he said, only if there are "severe supply issues and disruptions" related to national security.
War worries have caused crude prices to soar and the low inventories have added to the tight oil markets. The price of light sweet crude rose to a 26-month high this week on the New York Mercantile Exchange to $35.60 a barrel.
But some analysts said an easing of the supply crunch may come soon.
World oil output increased by nearly 1.2 million barrels a day in January, according to the International Energy Agency. Saudi Arabia and other OPEC producers agreed to boost production to try to make up for lost Venezuelan oil, and even Venezuela's output began to rebound.
"There's some crude oil from the Middle East arriving soon that could help build up stocks," said John Lichtblau, chairman of the nonprofit, New York-based Petroleum Industry Research Foundation. It takes about 40 days for Middle East oil to reach the United States.
While Venezuela's production, stymied by months of political strife, increased in late January, its exports remained sporadic and well below levels before the country's unrest.
The United States, which uses about 20 million barrels of oil and imported refined products a day, last year relied on Venezuela for 1.5 million barrels a day of crude as well as refined gasoline.
In its weekly oil summary, the Energy Department's Energy Information Administration said that while crude oil stocks fell, gasoline inventories rose by an equivalent of 3 million barrels. That is still well below normal.
Both demand for gasoline and for heating oil has been high, causing unexpected draws on both. Because of the cold winter, heating oil stocks in the Northeast were reported 35 percent below what they were last year.
By H. Josef Hebert