BP fought long and hard to avoid the defeat it suffered in court on Thursday when a federal judge ruled that the oil company was chiefly responsible for the Deepwater Horizon oil rig explosion, opening the door to new civil penalties that could potentially amount to $18 billion.

But analysts say that it could be years before the company pays any of those penalties and that they could turn out to be as low as $8 billion to $10 billion. And with the company expecting cash flow of $30 billion to $31 billion this year, the environmental payments will be stiff but not impossible to make.

“BP has been preparing for years to deal with anything like this,” said Stephen Simko, a Morningstar senior equity analyst, who noted that the company had sold off $38 billion in assets since the spill. “Their cash flows are growing, and this ruling can be appealed for years and years. It’s just a situation that is much more manageable.”

Investors agreed on Friday. After they dumped BP shares so heavily on Thursday that the company’s market value plummeted by roughly $8.5 billion, BP stock staged a modest comeback on Friday, closing 2.3 percent higher at $45.93, as investors concluded that the British-based oil company could weather this new gale in a four-year-old storm.

Still, the company faces uncertainty. Thursday’s ruling is the latest in a string of legal setbacks for BP as it tries to lower its fines and other payments to businesses and individuals affected by the spill, many of whom the company says are undeserving.

BP is also vulnerable in Russia, where it has large investments at a time when Moscow’s relations with the West are deteriorating.

And the company’s cash flow could tighten, especially if events in Russia and Ukraine continue to worsen and Western sanctions are tightened. If Rosneft, in which BP owns a 19.75 percent interest, is unable to raise capital in Europe in the future, that could deprive BP of billions of dollars in cash dividends over the next few years, making it all the more challenging for the company to augment the $3.5 billion it has set aside to pay the environmental fines it now faces.

The estimates of how much BP might have to pay vary so much because Judge Carl J. Barbier of United States District Court has yet to decide how much oil was spilled in the accident, which killed 11 workers and soiled hundreds of miles of Gulf of Mexico beaches.

Because BP was found to be, in legal parlance, grossly negligent, it can be fined up to $4,300 for each barrel spilled. The government gave an estimate in court of 4.2 million barrels spilled, leading to the roughly $18 billion maximum potential fine. BP’s estimate is nearly two million barrels lower, which would lead to roughly half the fine.

The company has said it will appeal Thursday’s ruling. If BP can persuade an appeals court that it was simply negligent — as Judge Barbier found was the case for its contractors on the rig, Halliburton and Transocean — statutory fines would be limited to $1,100 a barrel. That would be about $3,000 less per barrel than under Judge Barbier’s ruling.

BP has noted that previous judges have set a high bar for gross negligence, which amounts to willful misconduct. But Carl W. Tobias, a University of Richmond law professor, said it would be difficult to overturn the decision on appeal. “The judge heard two months of testimony and has lived with this case for years, so it will be very hard to show that his fact-finding was erroneous,” Mr. Tobias said.

But BP will also be able to appeal the total spill amount, which was the focus of the second phase of the trial. And in any event, no monetary awards will be set until the completion of the nonjury proceedings’ third phase, which is scheduled to begin in January. Once the penalty is set, the company will most likely be given years to pay it.

BP has already struggled to manage the financial fallout of the Deepwater Horizon tragedy, which not only sullied its reputation but also piled on costs that were enormous for even one of the largest oil companies in the world. Selling off oil and gas fields, pipelines and refineries, BP has set aside $43 billion to cover disaster-related costs. More than half of that has been allotted to the cost of litigation and claims, including $11 billion to compensate individuals and businesses that suffered losses.

But even as BP has paid out billions, it has remade itself into a more efficient operation. It recently made big oil and gas discoveries in Angola and Egypt and has ramped up new prospects around the world. Cash on hand at the end of the first quarter was $27.4 billion. On Thursday, its chief executive, Robert W. Dudley, signed a revised agreement with the Iraqi government that extends production from two oil fields in southern Iraq.

“We just don’t see skies clearing for BP over the next six months,” Gimme Credit, a corporate bond research firm, said in a letter on Friday. But it added that despite risks in Russia and the continuing legal struggle, “survival is not seriously in question.”