A year ago, aluminum companies were nearly buried under cheap Russian metal. But six months ago, major producing nations reached a global accord to cut production. Now, the London Metal Exchange's inventory is shrinking, and aluminum prices are rocketing. Industry leader Alcoa's share price soared to a 52-week high of 861/2 in mid-September. Rivals such as Alcan and Reynolds Metals are also recording big gains. But can the accord hold? With lots of unused capacity around, producers will be tempted to bring plants back onstream, jeopardizing their recovery.