Stochastic simulation of the direct economic costs of oil dependence in an uncertain future is proposed as a useful metric of oil dependence. The market failure from which these costs arise is imperfect competition in the world oil market, chiefly as a consequence of the use of market power by the Organization of the Petroleum Exporting Countries (OPEC) cartel. Oil dependence costs can be substantial. It is estimated that oil dependence costs to the US economy in 2008 will exceed $500 billion. Other costs, such as military expenditures or foreign policy constraints are deemed to be largely derivative of the actual or potential economic costs of oil dependence. The use of quantifiable economic costs as a security metric leads to a measurable definition of oil independence, or oil security, which can be used to test the ability of specific policies to achieve oil independence in an uncertain future. (C) 2009 Elsevier Ltd. All rights reserved.