The price for crude oil produced by the Organization of the Petroleum Exporting Countries (OPEC) dropped by nearly four dollars Monday, OPEC said Tuesday. One barrel (159 liters) of OPEC crude stood at 94.09 dollars Monday, 3.81 dollars lower than 97.90 dollars last Friday, according to a report of DPA. OPEC calculates an average basket price based on 13 important brands produced by cartel members.