Speculation was a driving factor in the price of oil getting so out of hand, and the loss of credit (the lifeblood of speculators) and the fears about the world wide economy (and the speculative short selling from that) has driven the price of oil far below an appropriate level. As we have seen from the commodities markets and the realestate market, Speculation (generally speaking) takes care of itself; a handful of people who get in early make a killing, while the majority of speculators stay in too long and get eaten alive when the market changes direction. On top of this, speculators often provide a necessary service in a market and take the other side of a hedge ... this enables oil companies to protect themself from oil dropping too far too quickly, and transportation companies to protect themself from oil rising too far too quickly
OPEC does try to manipulate prices, but (like most cartels) doesn't really have much power because the member countries became used to the spending that the high price of oil justified and the only way to maintain their standard of living is to pump out oil as fast as they can.
As far as alternative energy sources go ... There are several cultures within oil companies, those companies who see themself as a resource company (and have investments in other natural resources), companies that see themself as a chemical manufacturer, and companies that see themself as an energy company (and often have a lot of research towards alternative fuel sources). All of these companies have plans for what they will do as the world no longer needs oil, and in most cases there is really no need to stop alternative energy sources from comming.
