Moscow and Beijing have agreed on a price formula for Russian gas exports, the biggest stumbling block for signing a deal between the world\'s largest gas producer and the world\'s fastest-growing energy market, and a deal could be signed soon, a Gazprom official said on Tuesday, but admitted that prices had still not been finally agreed. \"The price formula agreed, there is still the issue of what is the starting point of that formula,\"  Russian gas export monopoly Gazprom Deputy Chairman Alexander Medvedev said. Gazprom wanted the same returns on deliveries to China as to Europe, which sources said meant a price gap of at least $100 per thousand cubic meters between Gazprom and China\'s negotiating positions. \"We hope very much that the event expected by everyone - the signing of the contract to supply gas - is in the offing,\" Medvedev said, but did not elaborate. Negotiations between the world\'s largest gas producer and the world\'s quickest growing energy market were constructive and the parties were listening each other, he said. Talks over what would be a massive energy deal have been going on since the two sides signed a framework agreement in 2009. Meanwhile, China has been diversifying its sources of supply.