Oil fell on Tuesday as rising output from the Middle East renewed concerns about global oversupply while economic data painted a negative backdrop for the outlook for demand.
Brent crude futures were trading 40 cents lower at $45.43 a barrel at 1234 GMT, retreating from earlier gains. U.S. crude futures were down 53 cents at $44.25 a barrel.
Iraq said its oil shipments from southern fields averaged 3.364 million barrels per day (bpd) in April, up from 3.286 million in March.
Production from top exporter Saudi Arabia was 10.15 million bpd in April, but sources said that it could soon return to a near-record level of 10.5 million bpd.
Iran is also raising output after its emergence from Western sanctions in January and has increased exports to almost 2 million bpd from a little more than 1 million bpd at the start of the year.
"There are enough supply stories out there to slow or temper any gains," Energy Aspects analyst Richard Mallinson said, though he added that lower supply from the United States should support prices in the longer term.
Demand worries are also back on the horizon, stoked by a 14th straight months of decline in Chinese factory activity in April. British manufacturing output, meanwhile, dropped to a three-year low and euro zone growth was forecast to be slower than previously expected this year.
U.S. production has dipped from a peak of about 9.6 million bpd in June 2015 to less than 9 million bpd now, government data shows.
That had helped to lift crude by nearly 70 percent from decade lows hit early this year and analysts said that further sporadic price falls are likely given the spike, including Brent crude's biggest monthly gain in seven years last month.
Preventing further weakness, the combined supply of the four crude oil grades that underpin the dated Brent benchmark price is expected to fall in June to its lowest in nearly two years, with loading rates for the Forties stream set to fall, according to programs from trading sources.
Earlier in the session it looked as though North Sea supply would rise as the Brent stream, another of the four crude grades that make up the benchmark, is expected to rise to its highest in four months for June. (Additional reporting by Henning Gloystein in Singapore; Editing by Keith Weir)