Lifeboat services reported that several people had abandoned the vessels following the collision, according to British media reports.
The IEA, which advises the world's biggest economies on energy policy, said global oil demand was poised to climb to a five-year high this year thanks to lower prices.
The International Energy Agency (IEA) said a move by the world's big oil exporters in OPEC, led by Saudi Arabia, to defend their market share "regardless of price" appeared to be working. The strategy was driving out costly, inefficient production from other parts of the world, it said.
Brent crude futures fell below USD 115 per barrel in Asia on Friday on signs of economic weakness across the globe, with doubts about more easing by the US Federal Reserve and renewed worries over Europe's debt crisis sapping confidence in the outlook for demand.
Brent crude held near USD 109 a barrel on Monday after better US jobs data and talk of stimulus measures by the euro zone to support growth, while more data was eyed for clues on the health of the global economy and the outlook for oil demand.
State-controlled CNOOC Ltd launched China's richest foreign takeover bid yet on Monday by agreeing to buy Canadian oil producer Nexen Inc for USD 15.1 billion, forcing Ottawa to decide whether security concerns outweigh its desire for foreign investment in its energy resources.
Brent crude oil fell on Wednesday on mounting concerns that European leaders would fail to solve the region's intractable debt crisis at a key meeting this week, offsetting tighter North Sea oil supply.
Brent oil futures rose further above USD 91 a barrel on Tuesday, lifting their premium against US crude sharply as a strike by Norwegian oil workers threatened to tighten North Sea supply, with no resolution of the work stoppage yet in sight.
Brent crude fell for a second session on Wednesday, weighed by the possibility of a release of strategic oil reserves by the United States and European nations.
Temporary outages at North Sea oilfields have subsided, including the UK's 200,000 Buzzard field.
The timing of the restart of four Brent oil and gas platforms in the North Sea remains unclear after they were shut on Saturday, a spokeswoman for operator Royal Dutch Shell said on Tuesday.