Oil cartel initials (4)
I believe the answer is:
opec
'oil cartel initials' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for opec that I've seen before include "International oil-producing cartel" , "Group of countries with a common oil policy" , "Group of petroleum producing countries, formed in 1961" , "Organisation intended to control the production and sale of petroleum" , "Cartel of oil-producing countries" .)