Organisation formed in 1961 to administer a common policy for the sale of petroleum (4)

I believe the answer is:

opec

(Other definitions for opec that I've seen before include "Group of oil-producing countries" , "Cartel of oil-producing countries" , "Organisation intended to control the production and sale of petroleum" , "[CRUDE OIL] suppliers?" , "International oil-producing cartel" .)

I've seen this clue in The Mirror.

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