World oil prices hit reverse gear on Friday after weaker-than-expected US economic growth data overshadowed the impact of a rescue plan for debt-ridden Greece, traders said.
New York's main contract, light sweet crude for delivery in May, dipped 71 cents to 79.82 dollars a barrel.
London's Brent North Sea crude for May slid 56 cents to 79.05 dollars per barrel.
Data showed Friday that the US economy -- a top global oil consumer -- grew at a slower pace than previously thought in the fourth quarter, as business and consumer spending slackened amid a fragile recovery from recession.
The world's largest economy grew by 5.6 percent in the October-December period, the Commerce Department said, revising downward an earlier estimate of 5.9 percent growth in gross domestic product.
The slower growth stemmed from downward revisions to business investment, inventories, and consumer spending, the department said.
Analysts had expected the world's largest economy to grow at 5.9 percent in the final quarter from 2.2 percent in the third quarter.
In earlier trade on Friday, oil won a boost from an EU agreement overnight to help Greece reduce its massive debt mountain.
"The decision by the European Union to provide a fiscal aid package to Greece spread economic optimism across the energy market and boosted investor... risk appetite," Sucden analyst Myrto Sokou said earlier Friday.
Prices were also boosted by investors returning to the market "around the 80 dollar per barrel mark," said Ben Westmore, a minerals and energy economist with National Australia Bank.
Prior to Friday, prices had been slumping since touching 82 dollars on Tuesday as the euro lost ground against the dollar due to concerns over the debt crisis in eurozone member Greece.
A stronger US dollar tends to dent oil demand because dollar-priced crude becomes more expensive for buyers using weaker currencies.
But the dollar weakened Friday after European leaders clinched a deal to rescue Greece, with a standby package of loans backed by the International Monetary Fund halting the euro's slide.
The historic pact -- which re-writes the eurozone rule-book -- was designed to "reassure all holders of Greek bonds" that European partners "will never abandon Greece," European Union president Herman Van Rompuy said.
The EU figurehead said all 16 eurozone nations, including Greece, had committed to "participate," which was also designed send a message to speculators not to simply switch their attentions from Greece to a new target in trouble, whether Portugal, Spain or Ireland.
More broadly, leaders further agreed on the need for stronger "economic governance" in Europe with strengthened penalties for countries that consistently breach EU fiscal rules.
