Benchmark oil for December delivery was down 75 cents to $85.53 a barrel in electronic trading on the New York Mercantile Exchange.
The contract had risen 23 cents to end at $86.28 a barrel in New York on Friday.
In London, Brent crude, which is used to price international varieties of oil, fell 55 cents a barrel to $109.01.
Forecasters say the massive storm system could blow ashore today across a wide swathe of the eastern seaboard, bringing with it the potential for massive flooding and widespread power outages.
New York City is in the direct path of the storm and expected to bear its brunt. Air, land and rail transportation was halted and hundreds of thousands of people have been ordered to evacuate.
The New York Stock Exchange and the New York Mercantile Exchange are shutting their trading floors in New York today, although trading will go on electronically.
While more than half a dozen refineries could be in the path of the storm, the US is well-supplied with oil while demand for petrol is down as large numbers of Americans remain unemployed and so don't drive to work. Oil is down 13% since hitting $99 in mid-September.
