By Gene Ramos

NEW YORK (Reuters) - Crude oil futures fell as much as 3 percent on Thursday, and are on track for the worst quarterly performance since the 2008 financial debacle, on worries that an EU summit will not find durable solutions to the euro zone crisis, stifling global growth prospects.

Lower U.S. equities following the U.S. Supreme Court decision upholding key elements of President Barack Obama's healthcare reform law added to the day's pressures on crude futures.

Despite recent gains, Brent crude futures were on track to end the second quarter down about 25 percent, the largest drop since the last quarter of 2008, which was the height of a financial crisis.

U.S. crude futures, meanwhile, were headed for drop of fall about 24 percent, also the biggest quarterly loss since the last quarter of 2008.

Trading on Wall Street was volatile, with large health insurers hit, after the Supreme Court upheld the centerpiece "individual mandate" provision of the Obama healthcare overhaul. Equities were already lower on skepticism that the European Union Summit will result in concrete measures. (.N)

U.S. equities later ended with pared losses on talk that EU finance officials were working on urgent measures to ease financial pressure on Spain and Italy.

"It's the euro zone problems, the strength of the dollar and the weak equities," said Stephen Schork, president of the Schork Group in Villanova, Pennsylvania, commenting on the reasons for the day's price drop.

The euro fell against the dollar on doubts about the outcome of the EU summit, denting investors' interest in buying riskier assets such as oil and other commodities. (USD/)

In London, Brent crude oil futures for August settled $2.14 lower at $91.36 a barrel, after a session low of $90.88.

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Oil heads for worst quarter since 2008 crisis