He has acquired at least 80% of Sibneft, one of Russia's largest oil companies.
"To read too much into this is like reading tea leaves, " said Sibneft spokesman John Mann.
He teamed up with Berezovsky to take over Sibneft at a fraction of its market value.
Last year, Gazprom, the giant state gas company, bought Sibneft, a private Russian oil producer.
Two big integrated oil firms, Yukos and Sibneft, said they were calling off a planned merger.
Yukos and Sibneft hope to construct their new holding company within six to eight weeks.
Abramovich counters that he already paid Berezovsky handsomely for his political clout and never promised ownership of Sibneft.
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Mr Berezovsky, 65, had claimed Mr Abramovich, 45, intimidated him into selling shares in Russian oil giant Sibneft.
Large and powerful companies, including Sibneft, Norilsk Nickel and Alfa Bank, were represented.
The Kommersant newspaper said on Monday that Gazprom could launch a joint bid for Sibneft with Royal Dutch Shell.
Yet while back-tax claims have wrecked Yukos, Sibneft seems to have settled a much smaller bill quietly and amicably.
In a similar vein, Sibneft used to brag about the advanced management and innovations introduced by its enlightened leaders.
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Abramovich (under oath, mind you) admitted that Sibneft sold to shadowy intermediaries (which he happened to own) at bargain-basement prices.
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Elf Aquitaine, a French energy company, last week pulled out of a planned alliance with Sibneft, a Russian oil firm.
In London, though, he's seen attending virtually every game, often with his wife and with fellow billionaire Sibneft President Evgeny Shvidler.
The duo had co-founded oil giant Sibneft in 1990s Russia, when the privatization of former state-owned assets made both men very rich.
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Sibneft was often in the news during Mr. Shuvalov's years in office.
The two fell out, with Berezovsky alleging that Abramovich blackmailed him into selling his Sibneft shares at a fraction of their market value.
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It is notable, too, that Yevgeny Shvidler, head of Sibneft, one of Mr Berezovsky's supposed assets, has signed the joint letter of protest.
Yukos produces more oil than it can refine, whereas Sibneft needs crude for its main refinery at Omsk, the biggest and best-equipped in Russia.
However, analysts took the move as a sign that Sibneft was preparing itself for a sale, after having earlier said it would pay no dividends.
He charges that Abramovich bullied him into selling his promised half stake in Sibneft for a fraction of its worth after his fall from favor.
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But, according to some critics, Sibneft has not grown up entirely.
Such a deal would certainly be good for Yukos-Sibneft, which would be able to get its oil out through a partner with world-wide distribution and refining facilities.
Then there was oil, in particular Sibneft, a large company now striving for respectability, whose spokesmen get tongue-tied when asked about Mr Berezovsky's exact role in it.
Up until early 2004, he also held an option on a 0.5% stake in OAO Sibneft, then a major Russian oil company, say people familiar with his finances.
Already, Sibneft, with Tyumen, controls nearly a quarter of Slavneft.
Yukos and Sibneft should both gain from combining their assets.
Later owning Sibneft, the national airline Aeroflot, and as primary shareholder in Russia's main television channel, he supported Boris Yeltsin's rise to power, enjoying huge influence during this era.
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That accolade goes to Sibneft, which would set up a new company every quarter into which it poured its profits, and which Sibneft would subsequently buy for a dollar.
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