Oil prices dropped on Friday as traders continued to book profits from a rally that sent crude futures to 2016 highs this week.

Oil prices dropped on Friday as traders continued to book profits from a rally that sent crude futures to 2016 highs this week.

The losses were in line with a big sell-off on European stock markets that was being fuelled by worries about the weak state of the global economy, traders said.

Around 1100 GMT, Brent North Sea crude for delivery in August was down 57 cents at $51.38 a barrel.

US benchmark West Texas Intermediate lost 62 cents to $49.94 a barrel compared with Thursday's close.

Despite Friday's losses and thanks to tighter supplies and a weaker dollar, prices have almost doubled since hitting near 13-year low points at the start of the year that had been caused by an excess of crude on world markets.

"A three-day winning streak came to an end yesterday," said oil brokers PVM in a note to clients published on Friday.

"The softer tone across energy markets weighed on global equities which also saw their recent run of gains grind to a halt as growth concerns returned to the fore," they added.