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