Oil price crisis: What is Opec? In 60 seconds
27 November 2014 Last updated at 17:07 GMT
The price of oil slumped after the Opec oil producers' cartel decided not to cut output at its meeting in Vienna.
Opec's secretary general Abdallah Salem el-Badri said the 12-member The Organization of the Petroleum Exporting Countries would not try to shore up prices by reducing production.
Following the announcement Brent crude fell below $72 a barrel, hitting lows previously seen in August 2010.
BBC News assesses the group, its history and the challenges ahead - in 60 seconds.
Video produced by Michael Hirst