U.S. crude settled below $44 for the first time since March on Friday, pressured by tumbling gasoline prices as the approaching end of the U.S. summer driving season suggested a growing surplus in fuel supply.
The U.S. benchmark West Texas Intermediate settled down 79 cents at $43.87 a barrel, near a six-year closing low of $43.46 reached in March.
Crude oil futures plumbed multi-month lows Friday and racked up a sixth straight week of losses.
Also weighing on prices was the latest rig count from oilfield services firm Baker Hughes, which showed U.S. energy firms added 6 oil rigs this week, continuing a recent trend of increases, even after U.S. crude oil prices plunged 25 percent from a recent high in June.
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The rig count gain this week was the third increase in a row, the longest winning streak since September 2014, bringing the total rig count up to 670, the highest since early May.
The dollar rose to a 3½ month high against a basket of currencies after strong U.S. jobs growth in July, putting pressure on oil and other commodities denominated in the greenback.
Brent, the global oil benchmark, has traded at six-month lows and U.S. crude at a 4½ month trough since Wednesday after government data showed U.S. gasoline stocks exceeding market estimates last week by about 300,000 barrels.
were 96 cents lower at $48.56 at 2:36 p.m. EDT (1836 GMT), near the lowest intraday level since January 29.
Analysts said seasonal refinery maintenance and stock builds in key oil products such as distillates, which include diesel, could drag heavily on crude futures in coming months.
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Gasoline sank by more than 1.4 percent to 5½ month lows on Friday, and ultra-low-sulfur diesel traded not far from six-year lows set earlier in the week.
"The summer driving season is fading and we could see a quick ramp up in gasoline stocks," said Chris Jarvis, analyst at Caprock Risk Management in Frederick, Maryland.
"We've had record refining heading out of the driving season that should translate into higher stocks of refined products in fall and winter."
The market is also awaiting Chinese trade figures over the weekend. Worrying data about the state of China's slowing economic growth, which has major implications for oil demand in the world's top energy consumer, has been a key factor driving the decline in oil prices in recent weeks.