U.S. oil prices sank 3.7 percent on Tuesday after Goldman Sachs suggested the recent rally was unsustainable and as analysts expected another U.S. stockpile build.
Comments from Goldman Sachs analysts that poured cold water over the prospects for a sustained rally also piled pressure on prices.
Differing views on a plan to limit oil output also put the market on the defensive. Kuwait, which produces 3 million barrels per day (bpd), said it will freeze output only if all major producers participate, including Iran, which has balked at the plan.
News of a meeting of Latin American crude producers set in Quito for Friday had boosted oil prices on Monday, and the bullish sentiment earlier swept over into Tuesday's session.
"The comments out of Kuwait have encouraged the sell-off and it appears likely that a focus on weekly oil inventories will encourage prices lower," said Matt Smith, director of commodity research at New York-based Clipper Data.
Brent crude futures were down $1.28, or 3.09 percent, at $39.58 a barrel, following six days of consecutive gains.
During the session it hit a 2016 high of $41.48, representing 50-percent rise from a 12-year low of $27.10 struck less than two months ago.
U.S. West Texas Intermediate (WTI) futures were settled 3.7 percent lower, or $1.40, at $36.50 a barrel, after briefly rallying to a three-month high of $38.39.
Goldman Sachs said rising oil prices "simply are not sustainable in the current environment".
The energy market "needs lower prices" to keep U.S. shale producers from ramping up output, Goldman said in a report. Otherwise, "an oil price rally will prove self-defeating, as it did last spring."
SEB chief commodities analyst Bjarne Schieldrop agreed, saying that falling U.S. shale oil rig numbers could soon rise again, halting the recent price rally.
A Reuters poll of oil analysts forecast that U.S. crude stocks likely rose 3.6 million barrels last week, pushing total inventories to a record high for a fourth week.
The American Petroleum Institute will release more preliminary stockpiles data at 4:30 p.m. EST (2130 GMT), before official numbers on Wednesday from the U.S. government's Energy Information Administration (EIA).
Separately, monthly loading programs suggest North Sea crude supply should hit a four-year peak in April, holding above 2 million bpd for an eighth consecutive month.
In a development that could support a further rally, the EIA said it expected U.S. production for this year to drop 760,000 bpd versus 740,000 bpd previously. It also cut its 2016 demand growth forecast by 80,000 bpd versus 110,000 barrels previously.
On the demand side, China's crude imports jumped 19.1 percent between January and February to 31.80 million tons, or about 8 million barrels per day, despite overall weak trading figures released on Tuesday.
"Higher 'teapot' (independent refinery) demand and stronger refining margins ... have contributed to increased imports. Falling domestic crude production is also supportive," said Virendra Chauhan of Energy Aspects.
China's February vehicle sales, a key driver for gasoline demand, were down 3.7 percent year on year, data from the country's Passenger Car Association showed.
"This is really a poor start for trade this year," said Zhang Yongjun, senior economist at the China Centre for International Economic Exchanges.