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Petrol patrol: A Russian soldier guards a pipeline.

Gazprom, Russia’s most powerful company, boasts several crown jewels: $83 billion in revenues last year, title of world’s largest gas producer, and its own major bank, television stations, and professional soccer team. Now, the energy giant can add another gem to that list: its own private army.

Citing the need to protect critical infrastructure such as pipelines and refineries, Gazprom and monster oil transporter Transneft recently convinced the Duma, Russia’s lower parliamentary house, to pass legislation allowing the companies to establish and arm their own security forces. The two state-run monopolies aren’t revealing the size of the proposed forces, but reports suggest that thousands of troops will be armed with machine guns and anti-riot gear. That’s particularly worrying news for countries in the region like Belarus, Poland, and Ukraine that are dependent on Russian energy and host to some of the companies’ facilities. “You don’t know what’s going on inside Gazprom,” says Lilia Shevtsova, a senior associate with the Carnegie Moscow Center.

That’s how the Kremlin likes it. In recent years, Gazprom has been used as a convenient—some would say coercive—tool of Moscow’s foreign policy, exercising leverage in the energy markets to further entrench the Kremlin’s power. Gazprom’s current chairman, Dmitry Medvedev, also serves as Russia’s first deputy prime minister and is widely rumored to...