OPEC members continuously cheat on each other. The reason oil prices collapsed in the early 1980s and stayed that way for two decades was because OPEC had no teeth. Somebody would always overproduce and reap the lion's share of the rewards, and then everyone had an incentive to overproduce.
OPEC also has an interest in keeping oil prices low over time. When oil prices are higher, people start investing in more efficient technology, reducing their overall need for oil, and consequently, OPEC's potential for political pressure.
