Moscow wants the Iran deal.   One of the reasons why sanctions against Iran will be lifted whether or not America pulls out of the nuclear deal is that the other signatories (Russia, China, and the EU) have an economic interest in lifting those sanctions. This economic interest includes natural gas.  On the face of it, there was no reason for Russia to let Iran re-renter the natural gas market.  The two countries, after all, are competitors.

Yet a closer look at the complicated geopolitics of energy makes sense of Russia’s endgame.  The EU imports about one third of its natural gas from Russia. This relative dependency limits the EU’s leverage over Russia and, therefore, Europe’s ability to rein in Vladimir Putin’s rampant annexation of eastern Ukraine. Since Iran has one of the world’s largest natural gas reserves, it could potentially help diversify Europe’s imports. Yet it might take a decade for Iran to turn into a major natural gas supplier (not least because Iran has a high domestic demand that is likely to increase). Putin, of course, understands that Iran might become a major competitor in this field, but he appears to assess that bringing back Iran into the natural gas market may help Russia create a cartel that will artificially inflate the price of natural gas. Doing so would serve Russia’s economic interests.