BP was continuing to test the cap over the oil leak in the Gulf of Mexico today after critical pressure checks on the blown-out well were extended for another 24 hours.
Integrity tests on the cap have been taking place since Thursday evening (Irish time) and were due to end last night.
But the tests – which will see whether the steel casing of the cap is sufficiently strong for the well to be shut off in the long term – will now continue throughout today, according to the official overseeing the response to the spill.
The oil giant said yesterday that the cap was continuing to hold – an announcement that will be greeted with cautious optimism after months of misery after the Deepwater Horizon rig exploded in April.
Following the final test, experts will begin to review the collected data to determine whether the leak has stopped for good.
News that the leak was stopped on Thursday helped BP shares soar around 8% higher at one stage on Friday, although wider stock market falls later pared the gains back.
David Cameron met BP chairman Carl-Henric Svanberg in Downing Street on Friday to discuss the latest developments.
The spill is likely to be high on the agenda in talks with President Barack Obama when the UK Prime Minister makes his first official visit to Washington next week.
The Financial Times reported that Mr Cameron is expected to defend BP during the talks, insisting that the group have a stable and strong future.
Mr Obama said the company’s breakthrough was “good news”, but warned there was still lots to do.
He said efforts would not stop until the leak – the worst in US history – was permanently stopped.
He warned BP would “pay for the damage it has caused” and added caution over early hopes for the progress in capping the leak.
“The American people should take some heart that we’re making progress,” he said.
However, he said there was still “a big job to do”.
“We won’t be done until we know we have killed the well and have a permanent structure in place.”
BP said last month that it was making a $20bn (€15.4bn) fund available for compensation.
The stock dipped below 300p at one stage last month – its lowest point since August 1996 – but recovered to more than 400p amid signs that it is closer to tackling the crisis, which has so far cost more than $3.5bn (€2.7bn) in spillage and clean-up.
The disaster began when the Deepwater Horizon rig exploded on April 20, killing 11 workers.
This year BP is not paying a dividend for the first time since the Second World War, although it insists it is financially strong enough to tackle the spill.
The group paid out about $165m (€127m) in claims to 52,000 businesses so far, although the intense political pressure on the oil giant eased after it set aside the $20bn compensation fund to meet the costs of the disaster in June.
Relief wells being drilled miles beneath the seabed will be the only means of permanently sealing and isolating the damaged well. The first of the wells is expected to be finished by the end of the month.
It is thought more than four million barrels of oil have so far flowed into the Gulf.