==+to describe world demand W and noncartel (competitive) supply S. Reasonable numbers for the price elasticities of world demand and noncartel supply are -1>2 and 1/2, respectively. Then, expressing W and S in millions of barrels per day (mb/d), we could write W = 160P- 1>2 and S = 131 3 2P1>2 Note that OPEC’s net demand is D = W - S.