Oil prices have declined sharply over the past three years. While both supply and demand factors played a role in the large oil price decline of 2014, global supply growth seems to have been the predominant force. The most important drivers were likely the surprising growth of US shale oil production, the output decisions of the Organization of the Petro-leum Exporting Countries and the weaker-than-expected global growth that followed the 2009 global financial crisis.