The aim of this paper is to determine if OPEC acts as a cartel by testing whether the production decisions of the different countries are coordinated and if they have an influence on oil prices. Relying on cointegration and causality tests in both time series and panel settings, our findings show that the OPEC influence has evolved through time, following the changes in the oil pricing system. While the influence of OPEC is found to be important just after the counter-oil shock, our results show that OPEC is price taker on the majority of the considered sub-periods. Finally, by dividing OPEC between savers and spenders, we show that it acts as a cartel mainly with a subgroup of its members.