London — OPEC is considering a new formula to govern failure oil price increases. The proposed formula would have the OPEC members make regular, quarterly increases in the price of their crude, which accounts for 90 percent of the volume entering world trade. The increases would in part be indexed to Western inflation and economic growth and to fluctuations in a basket of the dollar and eight other major currencies. Oil prices would also be made to rise to the level of costs for alternative energy sources. The proposal may be voted on during OPEC's November summit meeting.