The Globe and Mail reports in its Friday edition that the Iran war has made clear that China, long vulnerable to oil supply shocks, has turned that weakness into a surprising source of geopolitical power. A New York Times dispatch to The Globe says that China made that shift by stockpiling huge amounts of oil, building extra oil-refining capacity, and investing in coal and other alternatives. In the early months of the war, it flexed that power by cutting off supplies of jet fuel, gasoline and diesel to neighbouring countries. The threat that a foreign power would restrict the country's access to oil may no longer deter leaders in Beijing from taking aggressive steps like invading or blockading Taiwan, former U.S. officials said. As of late August, crude oil cost roughly $10 (U.S.) a barrel less than it would have had China continued buying at prewar levels, says Goldman Sachs. China's sway over the crude oil market differs from that of oil-producing countries because it imports more than it produces. It tends to reduce oil price volatility, lifting prices when it is stocking up -- as it was last year -- and easing them when it is not, as has happened since the war started, says Goldman Sachs.