Crude oil exports by OPEC in August were 25.19 million barrels per day (bbl/d), their lowest level since April, according to Thomson Reuters Oil Research.

But average 2017 levels for January-August of 25.05 million bbl/d were above average 24.85 million bbl/d in the same period a year earlier, despite OPEC's pledge to hold back supplies between January this year and March 2018 in order to tighten the market and prop up prices.

The drop of 370,000 bbl/d between July and August was largely a result of the political and economic crisis in Venezuela and disruptions in the group's African members, the research showed.

"Crude oil exports from OPEC's African members tumbled by 540,000 bbl/d month-on-month to below 5 million bbl/d after posting their highest export volumes in July since at least Jan. 2015, thereby breaking a four-month streak of rising exports," Thomson Reuters Oil Research said in a report published on Sept. 6.

The fall in African output may not be long-lived. Oil production at Libya's Sharara Field, the country's largest, was resuming on Sept. 6 after a valve was reopened on a pipeline shut by an armed group for more than two weeks, Libyan oil industry sources said.

For now, the fall in African output offset rising shipments from the Middle East, OPEC's biggest producer region, which rose from 18.06 million bbl/d to 18.34 million bbl/d between July and August.