“The complexity and the size of it is what creates a huge challenge for Russia and for Gazprom,” said Vitaly V. Yermakov, director of research for the Russian and Caspian region at Cambridge Energy Research Associates.

CRITICS say that Gazprom muscled its way into the ranks of the world’s energy giants with blatant and often ham-handed tactics, particularly during the Putin years. The Yuzhno-Russkoye field, which Gazprom points to as an example of its resurgence, is a case in point.

Richard W. Moncrief, a Fort Worth oilman, says he is the rightful owner of 40 percent of the field, which he says he bought in a series of agreements with Gazprom about a decade ago. But he says that Gazprom didn’t recognize his contract, instead granting BASF, a Germany company, a 35 percent stake in the field. Mr. Moncrief is suing Gazprom in Berlin, contending that his stake is now worth $12 billion.

Gazprom maintains that the agreements were not binding: “The company denies any obligations toward Moncrief Oil in relation to the Yuzhno-Russkoye field,” the company said in a statement.

Mr. Moncrief disagrees, but is pessimistic about his legal position.

“Nobody has ever gotten a Russian company into a court that could enforce a contract,” he said in a telephone interview. “In the end, the Russians are going to do exactly what they want to, and they’re going to ride the back of Western commerce to fund their country.”

Western executives say that the Kremlin is always on call whenever Gazprom needs a boost.

Last year, TNK-BP, a Russian joint venture involving BP and the Alfa Group, Access Industries and the Renova Group, agreed to sell Gazprom a vast Siberian gas field after Russian authorities threatened to cancel the venture’s license to operate there. Gazprom offered $700 million to $900 million for TNK-BP’s stake in the field and a local gas distribution company. It is a complex deal that has yet to close. Whatever its terms, analysts say, they would hardly compensate BP for the field, Kovykta, which is thought to hold immense gas supplies  and for the millions of dollars that the venture had already invested there.