The increase came despite efforts by the Organization of the Petroleum Exporting Countries and a handful of external producers to drain stocks below five-year averages and reduce global output by 1.8 million barrels a month until March 2018.
US crude inventories added 2.75 million barrels last week, while gasoline stockpiles increased by 1.79 million barrels last week, the API said Tuesday, according to people familiar with the data.
Meanwhile, the EIA has reported that shale production in the USA would reach an all-time high in July, at 5.475 million bpd and adding an additional rig to bring the total rig count to 719, continuing the twenty-two-week streak. New supplies from OPEC's competitors will be more than enough to meet growth in demand next year, the IEA said in a report Wednesday.
He said that USA refinery inputs hit a record last week, with the amount of crude processed at just over 1 million barrels a day more than the same time previous year.
WTI was trading up 0.8% at $46.45 per barrel at 3:11pm EST-more than $1.50 per barrel lower than a week ago-with Brent trading at $48.74, compared to $50.05 per barrel last week.More news: Iran says Saudis suspected of being behind terror attacks
Total OPEC Members' proven crude oil reserves increased by 0.5 per cent to 1,217 bn b at the end of 2016, with a share of 81.5 per cent of total world crude oil reserves.
Iraq has been India's second biggest supplier of oil for years. Resurgent US tight oil production has been regarded as the biggest threat to its efforts.
The group also cut its forecast for growth in the United States, where shale producers have gained impetus from the higher prices brought about by the cut.
ANZ bank said in a note to clients that prices were "under pressure earlier in the day after a report from OPEC showed that its production had increased".
With regards to the prices, the ASB indicated that the OPEC Reference Basket averaged $40.76/b in 2016, down from $49.49/b in 2015 and reaching the lowest yearly average since 2004.
China imported 12.5 percent more oil in the first four months of this year, but imports from Saudi Arabia rose by a paltry 2.5 percent.
"We think this effectively takes September off the table", said Ian Lyngen, head of USA rates strategy at BMO Capital Markets in NY, in reference to the impact of the data on the probability of a September Fed rate increase.