When the price of oil drops this usually means that opec has?

When the price of oil drops this usually means that OPEC or a major state within OPEC like Saudi Arabia, or Venezuela has increased the supply of oil leading to a drop in price. This is the current policy of the Saudi Government which has led to a drastic decline in oil prices over the last 3 to 4 months. 

Answeroil-shale;

Answer accretion;