This study considers what we call the ＇＇degree of optimality＇＇ of quota assignments for each OPEC member country bared on certain proposed ＇＇fairness＇＇ factors. We argue that these factors should ideally be based on energy and economic conditions that ought to be taken into consideration when production quotas are assigned. Thus, in this study, importance weights based on proven reserves, available productive capacity, GDP per capita and domestic investment needs are first obtained for allocating fair quotas to each member country in the period 1982-1990. Then a degree of fairness optimality index is computed for each member country and is applied to measure the performance of these countries during the quota system period. Our investigations reveal that OPEC appears to give greater importance to the energy factors, proved reserves and productive capacity, although domestic investment needs seem to play a significant role in determining the direction of quota assignments. Statistical tests reveal that all the weights are consistent over time. Finally, we observe that the member countries whose ideal quotas are based on low GDP per capita have higher degrees of optimality than those whose ideal quotas are based on proven reserves or available productive capacity. The computed importance weights and optimality measures can be used both by OPEC and energy analysts interested in OPEC behavior.