OPEC MEASURE is a term used to refer to the production quotas set by the Organization of the Petroleum Exporting Countries (OPEC) for its member countries. The two crossword solutions, BARREL (6 letters) and BBL (3 letters), refer to the unit of measurement used to determine the amount of oil produced by each country. A BARREL is a unit of volume equal to 42 US gallons, while a BBL is a shorthand version of the same unit.