The price for oil produced by the Organization of the Petroleum Exporting Countries (OPEC) stayed above the $50 mark on Tuesday, but still fell by nearly one dollar, the group announced on Wednesday. One barrel (159 liters) of OPEC crude stood at $50.96 Tuesday, 0.94 dollars less than on the previous day. The Vienna-based Group calculates a basket price based on 12 brands produced by its members.