Oil prices edged higher today after Opec left supply limits unchanged, but remained sensitive to weakness in equity markets, reflecting concerns about economic growth in the US.
US crude rose 17 cents to $57.95 by 1500 GMT..
London Brent crude was 57 cents higher at $61.24. Brent has risen to a premium to US crude because of production disruptions in Nigeria and a firm North Sea market.
Oil prices have been under pressure as troubles in US housing finance sector have heightened fears in world stock markets about the health of the economy in the US, the world's biggest oil consumer.
"The equity markets have been recently a leading indicator for the oil market," said Olivier Jakob, at oil research consultancy Petromatrix.
Investors are worried that a rising number of mortgage defaults by higher-risk borrowers in the US could affect the broader financial sector and consumer confidence.
Former Federal Reserve chairman Alan Greenspan warned on Thursday that defaults in mortgage markets could spill over into other economic sectors.
"There's a big cloud in the sky. The question mark is about the US. economy and concerns over the housing industry because that will have a big impact on consumer demand, which may affect oil consumption," said Andrew Harrington, an analyst at ANZ Bank.
Opec, which pumps more than a third of the world's oil, is also concerned about the implications of the equity market weakness.
"We are watching developments on world stock markets, to assess their possible impact on the global economy and, in particular, on energy demand," said Opec President and United Arab Emirates' Oil Minister Mohammed bin Dhaen al-Hamli.
Opec, as expected, agreed to keep existing limits on oil output at its meeting in Vienna yesterday.
It had already agreed cuts totalling 1.7 million barrels per day at two previous meetings. The cuts followed oil's retreat from a peak in July last year and helped prices to recover from a 20-month low of $49.90 on January 18th.
Opec's supply curbs have helped to balance supply and demand. Gasoline stocks, for example, have been falling in the United States since early February.