Russia and China had been trying to negotiate a deal for more than a decade; Russia holds the world's largest natural gas reserves, and China's demand for natural gas is rapidly growing. However, the deal was impeded by several factors, including the fact that Russia sent most of its energy west and that China focused on domestic production as it imported natural gas via foreign sea routes. But both countries' interests have aligned in recent years. For China, the cost of importing liquefied natural gas is high and its energy demands continue to grow. For Russia, the stability of demand from Europe — which is where Russia sends more than 80 percent of its natural gas exports — has been a growing concern, especially in recent months as Russia and the West have sparred over Ukraine.