2001 Nobel economics prize winner Joseph Stiglitz, meanwhile, said the new currency could come about quickly if it was based on an expansion of the IMF's already established system of Special Drawing Rights, units of exchange used by the IMF which already have some of the features of currency. Stiglitz argued that, as the US dollar has become the standard global reserve currency, it has inadvertently created a system which hurts the world economy. "It's a net transfer, in a sense, to the United States of foreign aid," he argued, reasoning that when other countries purchase US dollars in order to use them on international markets (such as for the buying and selling of petroleum), they effectively give the US a zero-interest loan — sometimes at times when they can least afford it. Stiglitz made his comments as head of a United Nations panel of economists giving recommendations to address the global financial crisis.