Oil came under pressure on Monday on signs a multi-week rally was encouraging a rejuvenation in already bloated U.S. shale supplies.
U.S. crude prices gained on a weekly basis for an eighth straight week last week while Brent had its first profit-taking in five weeks.
In a sign the market was responding to those gains, rigs for drilling oil in the voluminous Permian shale basin rose for the first time this year after months of cutbacks.
U.S. crude futures were down 49 cents at $58.90 a barrel by 11:48 a.m. EDT (1548 GMT).
Brent crude futures, the more globally referenced benchmark for oil, fell 85 cents to $64.54.
The market's drop was limited by China's third rate cut in six months which raised hopes the world's No. 1 energy consumer will help absorb some of the excessive crude supplies.
And despite the gains in the Permian Basin, the overall number of active oil rigs in the United States has declined for a 22nd week in a row, although the rate of decline has slowed lately.
"It's pretty choppy as people try to figure out a clearer supply-demand situation," Gene McGillian, senior analyst at Tradition Energy in Stamford, Connecticut, said, referring to Monday's action.
"I'm not entirely sure the rally of the past few weeks is behind us, so we could ultimately be setting ourselves up for an even sharper decline later," he added.
Hedge funds and other big speculators raised bets for a seventh week in a row last week that crude prices will rise, exchange data showed.
Analysts talk of a growing disconnect between the futures market, which has gained more than 40 percent since its January low, and a growing physical supply glut.
Analysts at Morgan Stanley (MS) said growing supplies in the physical market, signs of increasing activity in U.S. shale oil production and potential for higher OPEC output are weighing on the outlook.
"We have growing concerns about crude fundamentals in the second half of 2015 and 2016," the bank said in a note to clients.
Oil's recent rally also appears technically exhausted, chartists said, noting Brent's halted advance after it had hit 2015 highs last week.
Investors will be looking at Wednesday's monthly report from the International Energy Agency to see if falling oil prices have boosted global demand for oil.
(By Barani Krishnan; Additional reporting by Ron Bousso in London and Florence Tan in Singapore; Editing by Christopher Johnson, Jason Neely and Ted Botha)