Oil prices fell about 3 percent on Monday as production from OPEC neared all-time peaks and record speculative buying in global benchmark Brent sparked profit-taking on last month's outsized rally.
OPEC's crude production climbed in April to 32.64 million barrels per day, close to the highest in recent history, a Reuters survey showed.
Iraq's April exports from southern fields increased, as did seaborne exports from Russia, the biggest exporter outside OPEC.
Traders also cited market intelligence firm Genscape's report of a 821,969-barrel rise in stockpiles at the Cushing, Oklahoma, delivery point for U.S. West Texas Intermediate (WTI) crude futures during the week to April 29.
Brent's new front-month contract, July, settled down $1.54, or 3.3 percent, at $45.83 per barrel, hitting a session low at $45.72.
WTI closed down $1.14 cents, or 2.5 percent, at $44.78 a barrel, after hitting an intraday low at $44.54.
"Our high side parameters for both WTI and Brent have been achieved and we would strongly suggest against purchases anywhere across the energy spectrum, especially off the weekly EIA data," said Jim Ritterbusch of Chicago-based oil markets consultancy Ritterbusch & Associates.
The U.S. Energy Information Administration (EIA) will issue on Wednesday weekly supply-demand data on oil. Cushing stockpiles aside, U.S. crude inventories as a whole likely rose by 1.4 million barrels last week, a Reuters poll of analysts found.
Speculator bets on higher Brent prices reached record highs last week as Brent futures gained 21.5 percent in April, their largest monthly advance in seven years. Bets on WTI futures and options also rose, to 10-month highs, feeding investor views that prices may have risen too far, too fast.
"The recent rally in oil prices that took WTI above $46 a barrel appears to have little to do with fundamentals, only partially with financial factors, and possibly more to do with sentiment," BNP Paribas oil strategists Harry Tchilinguirian and Gareth Lewis-Davies said.
Morgan Stanley said it expected the drop in the U.S. rig count that helped crude prices recover to end soon as shale oil producers increase drilling. "History suggests a rig count bottom is imminent and increases are coming," it said in a note.
In Brent, Monday's volume was just about half of levels seen last week, with the market in London closed for the May Day holiday.
Brent's previous front-month contract, June, settled on Friday at $48.13 a barrel, after setting a six-month high at $48.50.
With its June contract expiry, the premium for Brent's front-month versus second, known as "backwardation," ended. The new front-month, July, is now at a discount, or "contango," to the second-month, August.