The oil giant BP is staring at two giant decisions.

First, this weekend its board is weighing an offer to sell one of its crown jewels — a 50 percent stake in a lucrative Russian oil joint venture — to Rosneft, the Russian oil company that is mostly state-owned. The structure of the roughly $26 billion deal, however, could leave BP and Rosneft closely entwined.

Second, the company has been in intense negotiations with the Justice Department over how big a fine it will have to pay to settle charges, possibly including criminal negligence, that have flowed from the blowout at BP’s Macondo well in 2010 that caused a massive spill in the Gulf of Mexico.

It is a pivotal moment for BP. In just two years, it has sold about $35 billion worth of assets ranging from a pair of U.S. refineries, gulf oil wells and some Kansas gas fields to exploration tracts in Egypt, Venezuela and Vietnam.

Tens of billions of dollars more are at stake now. If Rosneft buys BP’s half of TNK-BP, the Russian venture, analysts expect it to make a large cash payment, perhaps $17 billion, and give BP about a 15 percent stake in Rosneft. The settlement with the Justice Department hinges on the department’s threat to bring criminal negligence charges against BP that would raise fines from $1,100 a barrel to $4,300 a barrel. The latter fine could bring the cost to $19 billion.

Will BP have a different look after these staggering deals?

Fadel Gheit, an oil analyst at Oppenheimer & Co., compared BP to a pitcher after Tommy John surgery. “He’s never the same pitcher, but he could win championships still,” Gheit said. He said that if the Rosneft and Justice Department deals go through, BP will have lost about 20 percent of its assets, about 20 percent of its crude-oil production, and as much as $50 billion in cash in two years — similar to giving birth to an entire new major oil company.

In return, it would gain an element of stability and put the spill mostly behind it.

At the end of the day, however, the smaller BP will remain one of the world’s five oil giants, known as supermajors.

And its main strategic focus, ironically, will be on deep-water offshore oil exploration, the same enterprise that tripped it up more than two years ago. BP is the biggest leaseholder in the deep-water Gulf of Mexico, where it has six rigs operating. And BP has staked out positions off the relatively unexplored coasts of Brazil and India.

The sale to Rosneft appears to be the more imminent deal. The BP board is meeting this weekend to consider a Rosneft offer to buy half of the TNK-BP joint venture that BP has with AAR, a group of Russian oligarchs.

That joint venture has been a huge headache for BP, albeit a profitable one. The venture has paid $19 billion in dividends to BP since 2003, far more than BP’s original $8 billion investment. But bickering with partners has been constant. BP’s chief executive, Bob Dudley, who took the helm after the oil spill, had earlier been in charge of TNK-BP. He and the AAR partners battled over board appointments and dividends, and Dudley ended up hurriedly leaving Russia as the dispute escalated.

Last year, AAR blocked BP from teaming up with Rosneft to explore Russia’s Arctic, even though the Arctic program had been sealed with a ceremonial handshake from Russian President Vladi­mir Putin. The AAR partners said that under the TNK-BP joint venture agreement, BP could not do business in Russia without them.

BP and Rosneft offered to buy out AAR for $30 billion, but the group declined.

“The situation in Russia was unsustainable,” said J. Robinson West, chairman of PFC Energy, a Washington firm that advises major oil companies including BP. “The jury’s still out. But they had to do something and I think this is probably just about as good as it was going to get.”

AAR might be sorry now. Its new partner, Rosneft, is 75 percent owned by the Russian government and headed by Igor Sechin, a former deputy prime minister and former Putin aide. Gheit thinks Putin and Sechin might still be upset about the high-profile Arctic exploration deal.

Earlier this month, AAR switched its stance and said it would consider selling its shares or listing some of them in a public offering if Rosneft bought out BP. It said that Rosneft lacks BP’s expertise in oil exploration. It also lacks the cash to easily swallow both BP and AAR’s positions.

West said that BP, which already owns 1.8 percent of Rosneft, could end up in a stronger position in Russia as part of a company with growing prospects instead of the mature ones held by TNK-BP. Rosneft has a market capitalization of $75 billion and 22.3 billion barrels of proven oil reserves, nearly as much as U.S. total reserves.

“There are two tracks to this,” he said. “BP will have its own activities in Russia. And then it will be a shareholder working with Rosneft, as well.”

Meanwhile, BP is seeking to close the oil-spill chapter in the United States. Negotiations with the Justice Department have intensified, but an agreement remains elusive.

BP says that a series of mistakes by different companies and flaws in equipment were to blame for the spill.

But the Justice Department said in a sharply worded Aug. 31 New Orleans court filing that it would seek to prove “gross negligence and willful misconduct.” It said that “the behavior, words, and actions of these BP executives would not be tolerated in a middling size company manufacturing dry goods for sale in a suburban mall.”

BP also disputes the size of the spill, saying that after subtracting oil that was recaptured or burned, the size of the spill was 2.8 million barrels. The Justice Department figure is about 4.5 million barrels.

A Citigroup report on BP in September estimated that the fines could range from $5 billion to $19 billion. But Pavel Molchanov, oil analyst at the firm Raymond James, said that “a settlement for $18 billion wouldn’t be a settlement. It would be a capitulation.” He predicted a deal in the $10 billion to $12 billion range.

BP still has $8 billion available from the assets it sold to meet spill liabilities.

Many of those assets, especially oil-producing wells, fetched high prices, bolstered by high crude prices. But some fell short. Brian Youngberg, an analyst with the investment firm of Edward Jones, said BP ended up “almost giving away” its Texas City refinery to Marathon Petroleum. Although BP has fixed up the refinery, it remains haunted by a 2005 explosion there that killed 15 people.

Youngberg said BP had been hoping to sell it for more than $2 billion. After subtracting the inventories of crude oil and other items, he said, the effective price was no more than $700 million.

If the sale of its TNK-BP shares is completed, however, BP could suddenly have even more cash on hand. With the loss of its Russian dividends, it will be under pressure to spend it finding a new source of earnings.

“I hope and assume they have a plan,” Gheit said. “You don’t trade one of your star players and say afterwards that we’ll think about who will take his place.”

Gheit said some of the money might go into developing a handful of huge offshore discoveries BP had made in the Gulf of Mexico shortly before the spill, as well as the Macondo field itself. He said BP hasn’t developed them yet because it wants to settle with the Justice Department. In the worst-case scenario, Justice could seek to impede BP’s ability to buy and develop further federal leases.

Gheit said he also expects that once BP settles the oil-spill cases, it will look at buying another company.

“Plan B will be an acquisition,” Gheit said. “You cannot grow a company this size by dribs and drabs.”