Brent crude slipped below $107 on Friday to its lowest in 2012 as a worsening euro zone crisis and weak US economic data raised fears of a global slowdown that could dent oil demand.
Worries about the euro zone, already roiled by Greek political chaos, mounted as Spain slipped into a recession, pushing the euro to a four-month low while sluggish data out of the United States sent worrisome signs about a still-fragile recovery at the world's largest economy and top oil consumer.
Brent crude slipped to its lowest in 2012 after falling $1.09 to $106.40 a barrel by 0548 GMT. Front-month Brent is on track to post its largest three-week fall since May 2011.
U.S. crude was down 65 cents to $91.91, heading for its largest three-week fall since August 2011.
"We've got a bit of a perfect storm at the moment," Michael McCarthy, a markets strategist at CMC Global Markets in Sydney said, pointing to the worsening euro zone crisis, lower demand as industrial output slows and bloated crude inventories in the United States.
The debt crisis in the euro zone worsened as Spain's borrowing costs shot up while its troubled banks suffered a credit ratings cut. This added to worries of Greece's possible exit from the common currency group as it does not have a government to implement austerity measures in exchange for rescue funds.
Greece's exit has the "potential for a structural destruction to Europe," McCarthy said. "We have no idea how this will pan out."
He added that it was "way too optimistic" to expect a quick recovery in Europe as further credit downgrades will weigh on demand projections.
Asian shares tumbled on Friday and were set for their worst weekly showing since September while the euro hit a fourth-month low on euro zone worries. The dollar index rose 0.34 percent.
New claims for US jobless benefits last week held at levels suggesting sluggish growth in hiring and factory activity in the mid-Atlantic region contracted in May.
US crude prices were supported by expectations that the Seaway pipeline reversal would ease the oil glut at Cushing, Oklahoma, its delivery point.
The first crude oil was expected to flow on the reversed Seaway pipeline this weekend, a historic move to ease a Midwest oil glut and bring depressed North American crude prices closer to world market levels.
July Brent's premium to West Texas Intermediate (WTI) narrowed to $14.17. T he premium had ended at $18.90 on Wednesday, when the Brent June contract expired.
Morgan Stanley expects the price spread to stay at $10 or wider as growing crude and gas production in North America will continue to demand changes in existing infrastructure and oil flow, its analysts led by Hussein Allidina said in a May 16 note.
"Spreads will likely exhibit greater volatility going forward as new production comes online and pipeline projects are proposed, completed or canceled, changing pathways for incremental volume," the bank said.
US crude may bounce towards $96 next week as it has technically hit the bottom, McCarthy said, although a weaker demand outlook may push it down to $88 in the next month.
Investors are now eyeing a summit this weekend of G8 leaders and nuclear talks between world powers and OPEC-member Iran next week. Brent surged to above $128 a barrel in March on supply concerns amid tightening Western sanctions on Iran over its disputed nuclear programme.
The United States delayed a bill for new economic sanctions on Iran's oil sector after Senate Republicans blocked the legislation on Thursday saying they needed more time to study the bill. The surprise move drew anger from Democrats who wanted approval ahead of nuclear talks next week.
Leaders at this weekend's G8 summit will discuss pressures on global oil markets and options they could take in response, a top White House official said on Thursday, declining to specify whether a release of strategic reserves would be on the table.