Oil prices fell on Friday as the euro and equities tumbled on increasing gloom over economic growth and reinforced worries about Europe's debt problems, Reuters reported.
Despite the day's losses, Brent and U.S. crude futures posted small gains for the week. Prices rose earlier in the week on tropical weather threats to U.S. output and a ruling by Germany's top court briefly soothed euro zone debt fears.
The euro fell to a 6-1/2-month low against the dollar as risk aversion increased on news that a member of the European Central Bank's Executive Board will step down due to a conflict over controversial ECB bond-buying.
The dollar index, measuring the greenback against a basket of other currencies, gained more than 1 percent.
Dollar strength can pressure oil by making it less affordable for consumers using other currencies and by attracting investment to markets offering better returns.
U.S. stocks tumbled more than 2 percent as the ECB news reinforced concerns about the region's debt and as investors remained skeptical about how much of U.S. President Barack Obama's $447 billion proposal to generate jobs would make it through Congress.
'Worries about the economy are resurfacing. Oil is tracing the plunging equity markets and strong dollar,' said Gene McGillian, analyst at Tradition Energy in Stamford, Connecticut.
ICE Brent October crude fell $1.78 to settle at $112.77 a barrel, swinging from $110.93 to $115.17. Front-month Brent managed a fourth straight weekly gain, but rose only 44 cents, or 0.39 percent.
Brent fell under its 100-day moving average at $114.22 and the 60-day MA of $112.69, according to Reuters data, but bounced back ahead of its 30-day MA at $110.68.
U.S. October crude settled down $1.81, 2 percent, at $87.24 a barrel, having dropped as low as $85.64. U.S. front-month crude posted a third consecutive weekly gain, up only 79 cents, just under 1 percent.
The Brent premium to its U.S. counterpart was at $25.53 a barrel based on settlements, after reaching a record $27.23 intraday on Tuesday.
Brent trading volume was 23 percent above the 30-day average and slightly outpaced U.S. crude volume that was 15 percent below its 30-day average.
Speculators cut their net long U.S. crude oil futures and options positions in the week to Sept. 6, the U.S. Commodity Futures Trading Commision said.
U.S. gasoline and heating oil futures also fell. Gasoline ended nearly 4 percent lower after last Monday's Labor Day holiday, the traditional end of the U.S. summer driving season.
Also bearish for oil, especially Brent, was news that about 2 million barrels of Libyan crude have been offered via a tender, the largest volume to come to market since civil war erupted in February.