Updated from 11:34 a.m EST
Crude oil prices closed slightly lower Friday, after another 5% rally Thursday, in what's become a market of wild swings in recent weeks.
The February futures contract shed 13 cents to $45.43 in Nymex floor trading.
Friday's decline comes amid a prolonged period of unseasonably warm weather in parts of the northern U.S. and growing market speculation about additional supply cuts from OPEC.
One force driving Thursday's rally was signs that the cartel's members had implemented previously agreed production cuts as part of a 1-million-barrel-a-day reduction.
OPEC next meets Jan. 30 in Vienna.
Just two days ago, prices fell sharply after the latest U.S. government data showed a greater-than-expected increase in crude oil distillate supplies, which include heating oil.
The supply-and-demand equation for heating oil is a major market focus at this time of year, with weather forecasts for North America and Europe playing a key role.
Prices have been unusually volatile in the past two weeks with moves of 4% to 5% in one direction or another.
The benchmark U.S. crude is down about 20% since touching a record high of more than $55 a barrel on Oct. 26, 2004. Nevertheless, oil prices are about 33% higher than a year ago.