OPEC has long been Saudi Arabia reducing output, and everyone else selling everything they can. They haven't had much power since the 1970s, but that they exist means they are a threat that if everyone else actually stuck to the agreement for a change. This is the common problem for cartels: everyone has inventive to cheat on the deals made. By selling a little more than your share you get more money, while because e…
So if the other side overpumped by x1 amount then you pump an extra x1 the next turn / year (maybe multiplied some reference production factor as they don't all have the same absolute limits).