In bleak times, there is a boom in doom. Americans have long been fascinated by disaster scenarios, from the population explosion to the cold war to global warming. These days the doomers, as Mrs. Wilkerson jokingly calls herself and likeminded others, have a new focus: peak oil. They argue that oil supplies peaked as early as 2008 and will decline rapidly, taking the economy with them. Located somewhere between the environmental movement and the bunkered survivalists, the peak oil crowd is small but growing, reaching from health food stores to Congress, where a Democrat and a Republican formed a congressional peak oil caucus.