Gazprom, they say, despite its market dominance, may need European customers even more than Europe needs its gas. That is because changes in the global energy market in the last year have weakened Gazprom financially, while also creating more potential alternative sources of supply.

The European Union is “in a stronger position to take on Gazprom than it has been before” said Christopher J. Weafer, a senior partner at Macro-Advisory, a Moscow-based business consulting firm. He noted, for example, that gas production in Azerbaijan would be coming online at the end of this decade. And he cited the potential of gas from Iran, if sanctions against that country were lifted. Iran has gas reserves comparable to Russia’s.

Europe “seems intent on putting a cap on Gazprom’s position,” Mr. Weafer said. “They can do that.”

Gazprom could eventually face a fine theoretically running higher than 10 billion euros, or about $10.7 billion. But the larger worry for Gazprom is the prospect of being forced to allow more competition in markets it has long controlled.

Mr. Weafer said that one of the few levers Gazprom might have in opposing the antitrust case would be to refuse new contracts to European customers, but that “that would be pretty much cutting off their nose to spite their face.”

Specifically, the European Commission, the European Union’s executive arm, said that unfair pricing might have resulted in higher gas prices in Bulgaria, Estonia, Latvia, Lithuania and Poland — countries that have long been wholly or substantially dependent on Russian gas. In those countries, the commission said, Gazprom was suspected of charging wholesalers prices that were significantly higher compared with the company’s costs or to benchmark prices.