Oil prices slipped on Thursday from four-year highs reached the previous session, pressured by rising US inventories and after sources said Russia and Saudi Arabia struck a private deal in September to raise crude output, reports Agencies.
Brent crude oil futures were trading at $86.14 per barrel at 0651 GMT, down 15 cents, or 0.2 per cent, from their last close.
Brent on Wednesday hit a four-year high of $86.74 a barrel, lifted by expectations of a tightening market ahead of US sanctions that will target Iran's oil exports from next month.
US West Texas Intermediate (WTI) crude futures were down 18 cents, or 0.2 per cent, at $76.23 a barrel.
"Data for last week showed a much more significant than expected ... build in US commercial crude (inventories), which generally suggests that oil prices should tumble," said Stephen Innes, head of trading for Asia-Pacific at futures brokerage Oanda in Singapore.
US crude oil stocks rose by nearly eight million barrels last week to about 404 million barrels, the biggest increase since March 2017, Energy Information Administration data showed on Wednesday.
US weekly Midwest refinery utilisation rates dropped to 78.9 per cent, their lowest since October 2015, according to the data.
US crude oil production remained at a record-high of 11.1 million barrels per day (bpd).
"This on top of the other big news of the day from Riyadh that ... Saudi Arabia and Russia will boost output," Innes said.
Russia and Saudi Arabia struck a private deal in September to raise oil output to cool rising prices, Reuters reported on Wednesday, before consulting with other producers, including the rest of the Organisation of the Petroleum Exporting Countries (OPEC).
Russia's and Saudi Arabia's actions come as markets have heated up ahead of US sanctions against Iran's oil sector, which are set to kick in from Nov 04, and which many analysts expect to knock around 1.5 million bpd of supply out of markets.
On the demand side, there is increasing concern that high oil prices and weakening emerging market currencies are creating a toxic inflationary mix that could erode fuel demand and economic growth.
Meanwhile, Russian President Vladimir Putin said on Wednesday an oil price of $65 to $75 per barrel would "suit" Moscow, as crude soared this week to reach the highest level since November 2014.
"A price of $65 to $75 per barrel would suit us. This would be completely normal to ensure the efficient functioning of energy companies and the investment process," the Russian leader told an energy forum in Moscow.
Oil prices spiked this week to a four-year peak, with Brent Crude at nearly $85 per barrel on worries over stretched global supplies due to US sanctions on Iran.
Energy firms enjoyed big gains on the surge, after the world's top producers agreed to maintain output despite pressure from US President Donald Trump.
Trump accused OPEC - the Vienna-based oil producing cartel - of inflating crude prices and hurting consumers.
"President Trump said that the price is high. He is partly right," Putin said.
"But such a price of oil is in large part the result of the current American administration's irresponsible policies, which directly affects the world economy," the Russian leader added.
OPEC and its non-cartel partners - including Russia - agreed at the end of June to increase production after a previous agreement at the end of 2016 had limited supply to support prices.