Benchmark Brent futures were down $1.36, or 2.8 percent, to $46.75 a barrel at 1:35 p.m. EDT (1735 GMT), after falling to $46.28, the lowest in more than a week.

US West Texas Intermediate (WTI) crude futures traded down $1.28, or 2.8 percent, at $44.24 a barrel, after falling to $43.78.

After rising earlier in the week, both benchmarks were headed to weekly drops of more than 2.5 percent, a sixth weekly decline in the past seven.

"The stream of relentless supply continues," said Matt Smith, director of commodity research at Clipperdata.

He noted OPEC exports were 2 million barrels a day higher in June than in 2016, despite a May extension of a 1.8 million barrel a day production cut led by the Organization of the Petroleum Exporting Countries.

"We've seen exports last month from OPEC much stronger than they were in April and May, seemingly indifferent to the OPEC production cut deal," Smith said.

Reuters oil data showed OPEC production is now at the highest level this year.

Russia, which is cooperating with OPEC in a deal to stem production, said it was ready to consider revising parameters of the deal if needed.

A group of oil-producing countries monitoring the deal will meet on July 24 in Russia, when they could recommend adjusting the pact.

US drillers added seven oil rigs in the week to July 7, energy services company Baker Hughes announced on Friday. This brings the total count up to 763, the most since April 2015.

On Thursday, weekly US government data showed that US oil production rose 1 percent to 9.34 million barrels per day (bpd) after a drop the previous week due to maintenance work and storm shutdowns.

"It takes somewhat lower prices to slow down US production," said Rob Haworth, senior investment strategist at US Bank Wealth Management.

Amidst rising US production, the market largely ignored news from the US Energy Information Administration (EIA) that US crude inventories fell by 6.3 million barrels in the week to June 30 to 502.9 million barrels, the lowest since January.

US bank Morgan Stanley said it expected WTI prices to remain below $50 until mid-2018.