Leak is plugged but storm has not abated for BP

In the case of BP's Gulf of Mexico catastrophe, the oil industry terminology of a "relief well" is aptly named. The ruptured Macondo well may have stopped pumping out oil into the Gulf of Mexico on 15 July. But only on Sunday was the "kill" operation finally completed and the biggest oil spill in history finally permanently contained.

The sense of relief at BP – which has lost more than $70bn (£45bn) of its market capitalisation, sacrificed its chief executive and still faces an uncertain future in the vastly oil-rich US coastal waters – is palpable. But the consequences of the explosion on the Deepwater Horizon rig in April that killed 11 people and unleashed the slick are far from over.

So far, the cost of the clean-up response has reached $9.5bn. Another $639m has been paid out to settle 146,000 civil claims against the company, a slug of them via the independent Gulf Coast Claims Facility managed by the high-profile dispute lawyer Ken Feinberg and funded by $20bn that BP is placing in an escrow account for such a purpose.

Despite the 4.1 million barrels of oil that spewed into the Gulf and threatened the fragile Louisiana wetland coast, BP looks like it has avoided the absolute meltdown that some were predicting when environmental devastation was headline news every night and the chief executive, Tony Hayward, was public enemy number one across the US.

"Macondo will become just another of the failures and resurrections that characterise the oil industry," one industry expert said. "BP has managed to avoid a complete corporate catastrophe – partly by finally capping the well, and partly by doing a deal with the US government over the escrow account that took responsibility for the fall-out and not trying to walk away."

That said, there are still significant hurdles ahead, which will need all the experience of Mr Hayward's replacement – the famously softly spoken Bob Dudley, who cut his teeth running the oil giant's fractious Russian joint venture – when he takes over next month.

While regulators around the world are looking at ways to tighten up safety procedures for off-shore drilling, raising the costs in the process, the biggest uncertainty for BP is how much of a kicking it will get from the myriad of official investigations into the Deepwater disaster.

So far BP's share price, after jumping by more than a third when the well was first sealed in late July, has remained relatively flat. There is a growing chorus – including the legendary US oil investor T Boone Pickens – that the stock is cheap and that compensation costs will come in far below the $20bn estimate. But the uncertainty on the thorny issue of negligence is keeping investors cautious. And even yesterday's rise of 2 per cent to 411.35p takes the stock nowhere near pre-explosion levels of nearly 650p.

Of the raft of inquiries underway in the US, the biggest is that by the Marine Board, which includes input from the US Coastguard and the Bureau of Ocean Energy Management. But there are also investigations by the Department of Justice, the Chemical Safety Board and the Environmental Protection Agency, as well as a Presidential Commission and a slew of state-level probes.

If BP is found guilty of gross negligence, the consequences will be ruinous: as much as quadrupling the size of the fine (which could balloon as high as $18bn) and devastating the company's reputation. But such an outcome is looking increasingly unlikely. BP's internal report, earlier this month, concluded that a total of eight separate faults or oversights contributed to the explosion, with responsibility shared between BP, the rig owner Transocean and the contractor Halliburton. The findings and their justification will feed into the US inquiries and have set the tone of the debate.

"It will be hard to prove negligence, although that is still a risk at this stage," Tony Shepherd, an analyst at Charles Stanley, said. "The biggest uncertainty for BP is whether the US attitude to the company, which has been very hostile up until now, will continue, or whether the official investigations will be less aggressive and exonerate the company to some extent."

Even then, Deepwater will not be over. First is the issue of compensation. Notwithstanding the views of T Boone Pickens and others on the size of the bill, the process will drag on the company's ability to move on from the disaster. "There might be an appetite to wrap all this up within months, but the reality of the litigation process could make it years or even decades," Richard Griffiths at Evolution Securities said.

Second is the future of the company in the US. The rhetoric against BP may show signs of calming down. But proposals were passed by the House of Representatives in July that would use the company's poor safety record – already marred, before Deepwater, by the Texas City refinery fire that killed 15 people in 2005 – to ban the company from further offshore drilling. For a company that produces more than a quarter of its global daily output in the US, and has plans for another 160,000 barrels per day from the region by 2020, the consequences would be calamitous.

With the November mid-term elections looming, and the Democrats facing a drubbing, the enthusiasm for such measures may yet wane. But even if not, the government may not have such freedom of action. BP is a world leader in technically challenging deepwater drilling, and the oil-thirsty US will need that expertise in the ultra-deep Gulf of Mexico. It is also one of only a handful of companies that can afford the rising costs of boosted safety regulations and plans for an up-front emergency fund.

"The bigger picture for the government is that it needs the big oil companies, because they are the only ones that can act as their own fire brigade," Mr Griffiths said.

The next six to 12 months will be crucial for BP, as both technical and legal investigations into the disaster start to conclude, and Mr Dudley sets out his plans to reshape the company. The leak may finally be capped, but the consequences have barely begun.