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, Reuters reported.
International Brent crude oil futures LCOc1 were trading at $53.66 per barrel at 0242 GMT, down 28 cents, or 0.52 percent, from their last close.
U.S. West Texas Intermediate (WTI) futures CLc1 were at $50.92, down 14 cents, or 0.27 percent.