Barrel bloc letters (4)

I believe the answer is:

opec

(Other definitions for opec that I've seen before include "Cartel of oil-producing countries" , "International oil-producing cartel" , "Group of oil-producing countries" , "Group of petroleum producing countries, formed in 1961" , "[CRUDE OIL] suppliers?" .)

I've seen this clue in The Washington Post.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.