Oil prices fell in thin pre-holiday trade Thursday after news of rising US crude reserves, while talks over crude producer Iran's nuclear programme dragged on, analysts said.
Brent North Sea crude for delivery in May edged down 12 cents to $56.98 a barrel around midday in London.
US benchmark West Texas Intermediate (WTI) for May slipped 25 cents to $49.84 a barrel compared with Wednesday's close.
"Prices have come off with thin volumes ahead of the holiday tomorrow," Michael McCarthy, chief market strategist at CMC Markets in Sydney, told AFP.
Financial markets in major crude trading hubs including Singapore, the United States and Britain will be closed on Friday for the long Easter holiday weekend.
McCarthy said dealers were still digesting the latest US Department of Energy's weekly petroleum report released on Wednesday.
The report, for the week to March 27, showed another increase in crude oil inventories to a new record high of 471.4 million barrels.
But it also revealed a slight decline in US production of 36,000  barrels per day, ending a long climb to record output levels that have contributed to the global supply glut.
"Crude oil prices posted renewed losses ... following a bearish weekly DOE oil inventories report which confirmed a large build in crude oil stocks," added Sucden analyst Myrto Sokou on Thursday.
"The bearish oil fundamentals currently weigh heavily on market sentiment, verifying a decline in US oil demand."
Meanwhile, talks between Iran and world powers aimed at preventing Tehran from getting a nuclear bomb remained in focus.
"We are a few metres... from the finishing line, but we are well aware that the final metres are the hardest," French Foreign Minister Laurent Fabius told reporters as he arrived late Wednesday back in Switzerland to rejoin the negotiations.
The five permanent members of the UN Security Council -- the United States, China, Britain, Russia and France -- plus Germany hope a full agreement, due to be finalised by June 30, will see Iran scale back its nuclear capability, which would prevent Tehran from developing a nuclear weapon.
In return, the diplomatically isolated Islamic republic, which denies wanting to build a bomb, is demanding the lifting of sanctions that have strangled its energy-reliant economy.