Cheating in OPEC has happened before and used to be fairly common. Saudi Arabia is growing concerned over hydraulic fracturing increasing US reserves that they want to drive down prices to prevent entry into the market. IRAN, VENEZUELA and other despots need $$ to support their failing economies so want prices high. It should get interesting.
It is also worth noting that the declining value of the dollar and the prospect that it will continue to do so has an impact since the price of oil is pegged to the dollar.