A British rig was expected to start drilling for oil off the Falkland Islands today, despite fierce opposition from Argentina.
Desire Petroleum's platform Ocean Guardian has been towed 8,000 miles from Scotland to the south Atlantic isles for the exploration.
Argentina has formally objected to the move and tightened shipping regulations in the region, but Britain has said any drilling off the islands is in accordance with international law.
Desire Petroleum is operating around 60 miles north of the main archipelago, where it estimates there are 3.5 billion barrels of recoverable oil as well as nine trillion cubic feet of gas.
Argentina's president Cristina Fernandez maintains The Falklands - coveted as Las Malvinas by Buenos Aires - are occupied by Britain illegally.
She also said the UK had failed to comply with United Nations resolutions requiring negotiations on their future.
But a spokesman for Desire Petroleum said the rig was sitting "firmly inside UK waters".
David Willie told the BBC: "Desire is an oil company and it's exploring for oil and not getting involved in what Argentina is saying about going to the UN."
Even if commercially viable amounts are found, it is expected to take many years before the oil production starts.
Last week the row between Britain and Argentina flared up ahead of the drilling operation, thanks to President Fernandez's decree requiring that any boat travelling to or from the islands get prior permission from her country.
But Prime Minister Gordon Brown backed the drilling operation, saying the UK was "perfectly within our rights to do this".
Argentina invaded the Falklands in 1982, before a UK taskforce seized them back control after a short war which claimed the lives of 255 British servicemen and women and more than 600 Argentinians.