Front-month Brent crude futures LCOc1 were down 45 cents, or 0.8 percent by 0951 GMT (4:51 a.m. ET) from their last settlement at $53.49 per barrel. The contract was up more than 13 percent this week, its biggest gain since March 2009. U.S. West Texas Intermediate (WTI) futures CLc1 were at $50.68, down 38 cents.

For China’s beleaguered oil sector, a deal by the Organization of the Petroleum Exporting Countries to cut output could offer a lifeline to an industry that has been hammered by low prices—and may also hasten its shift away from a heavy reliance on Saudi crude.

Shares in US oil companies soared on Wednesday as Opec ministers meeting in Vienna agreed a plan to cut output by 1.2m barrels per day. “The biggest beneficiaries from this Opec move are the US shale players,” said Mike Kelly, head of exploration and production company research at Seaport Global Securities.

OPEC in its 171st ordinary meeting on Wednesday, November 30, agreed to Iran's share of 3.9 million barrels per day in its total output.

The government of Iraq is hoping that a new OPEC deal will help the war-weary country generate enough revenue to help pay for its costly, 2-year-old fight against the Islamic State group. Iraq, whose oil revenues make up nearly 95 percent of its budget, has been reeling under an economic crisis since late 2014, when oil prices began their descent from a high of above $100 a barrel.

Oil prices slipped on Friday as some investors opted to cash out after Brent touched 16-month a high on Thursday, with optimism over this week's OPEC-Russia accord on cutting output giving way to questions on the "sticking point" of implementing the deal.

Russia promised to support a push by the Organization of Petroleum Exporting Countries to reduce a global oil oversupply after the group agreed to cut production by 1.2 million barrels a day on Wednesday. Energy Minister Alexander Novak pledged Russia would cut its own output by as much as 300,000 barrels a day, a stronger move than the previously preferred position of a freeze.

Accordingly, and in line with the ‘Algiers Accord’, the Conference decided to implement a new OPEC-14 production target of 32.5mb/d, in order to accelerate the ongoing drawdown of the stock overhang and bring the oil market rebalancing forward. The Agreement will be effective from January 1, 2017.

U.S. crude oil CLc1 added to overnight gains of 9 percent to reach $50.00 a barrel for the first time since October. Brent crude LCOc1, which soared $4 overnight, touched a six-week peak of $52.73 a barrel.

OPEC will reduce output by about 1.2 million barrels a day by January, the group said, fulfilling a plan sketched out in Algiers in September to cut its production to 32.5 million barrels. The agreement exempted Nigeria and Libya, but gave Iraq its first quotas since the 1990s. West Texas Intermediate crude futures rose 0.3 percent to $49.61 a barrel at 11:44 a.m. Singapore time after gaining 9.3 percent Wednesday, the biggest one-day gain since Feb. 12.