NEW YORK (Dow Jones)--Oil futures prices tumbled 1.6% Friday, unable to sustain a breach above $90 after flirting with the level this week.

Light, sweet crude for October delivery dropped $1.44 to settle at $87.96 a barrel on the New York Mercantile Exchange. Brent crude for November delivery also lost ground on the ICE Futures Europe exchange, dropping 8 cents, or 0.1%, to $112.22 a barrel.

Lower Friday volume and traders closing out positions ahead of the weekend made for a volatile session, with prices down as much as $2.40, or 2.6%, at one point before recovering somewhat to finish the day. Traders said seesawing U.S. equities markets, continuing uncertainty about euro zone sovereign debt and a strengthening dollar were behind the pullback--and contributed to the price swings.

With Friday's close, crude gave up most of the gains it had made during the week despite hitting a one-month intraday high of $90.52 Tuesday. It has neared or inched over the $90 level six times this month. But each time the price has retreated, disappointing traders who were hoping for a stronger bull run.

"Crude had approached the top end of its range here, right around the $90 level, and so far has not been able to punch through," said Matt Zeman, market strategist at Kingsview Financial. "At this psychologically important $90 level, there are a lot of willing sellers.

"It'll be interesting to see what happens in the next couple sessions," he added. "If this market cannot punch through $90, you might see a lot of selling resume. We're just kind of in no man's land right now, waiting to see which way this market will go."

The dollar rose 0.4% to 76.596 on the ICE Dollar Index, which tracks the greenback against a basket of other currencies. A stronger dollar cuts crude prices by making the dollar-denominated commodity costlier for holders of other currencies.

Though central bankers this week vowed to backstop European banks wrestling with sovereign debt problems, the market remains pessimistic about the crisis, market observers said. Furthermore, a spate of weak U.S. economic data this week is raising doubts about U.S. prospects.

"I think the real key worry for the oil markets is that we're heading into another downturn," said Bill O'Grady, the chief market strategist at Confluence Investment Management. "It's a very legitimate worry."

October reformulated gasoline blendstock, or RBOB, rose 28 cents, or 1%, to $2.7856 a gallon. October heating oil dropped 19.6 cents, or 0.7%, to $3.0050 a gallon.