The reasons I've heard were to kill US oil exploration, and also to teach the high-cost producers (Venezuela, etc) in OPEC a lesson. It's common for these count

The reasons I've heard were to kill US oil exploration, and also to teach the high-cost producers (Venezuela, etc) in OPEC a lesson. It's common for these countries to "accidentally" pump over quota to make some extra cash. So Saudi just refused to cut the quota this time around. The Saudis could also be interested in messing with Iran, which has much higher production costs.