I have only skimmed most of the above responses, so I apologize if I repeat anything.
1. You’re talking about betting your own personal, metaphorical farm (or 80–90% of it) on one thing. This is almost never a good idea, no matter what the thing is. It pretty much gives you one chance to make it or blow it; are you feelin’ lucky, punk? ;)
2. Unless you work in this industry every day like an insider, you are an amateur betting against the pros. Do you feel confident that you know more than they do? (Mr. Laureth, a fan of trading stocks, has likened futures trading to “going into the bad wolf kennel while wearing Milk-Bone underwear.)
3. With futures, you either need to trade the contract before the delivery date, or you need to take delivery of the product. Do you have a place to store a lot of oil? Those who trade in futures usually do.
4. Finally, the Peak Oil situation is whole lot more complex than “once you reach peak, it goes nowhere but up, up, UP!”. In fact, one way we can identify the peak is price volatility. Demand fluctuates wildly as people move to new energy sources or improve efficiency. Supply, no longer stable, has peaks and troughs as wells dry up or small discoveries are made, but it’s not the smooth flow of product that we’re used to. Are you willing to bet your future on something so volatile?
5. Oil may be a bubble as well. If you watch your investments like a hawk, daily readjusting them, you might possibly play the market to your advantage. Are you the sort of person who is willing to do this, or would you rather park it somewhere and relax, play with the kids, sleep at night?
6. It may be best to pick something else you think the world, or you, will need in the future. Or at least diversify, with some stable investments to offset any losses on oil as prices rise and plummet. I’m not making any promises and I am far from expert. But I think other options are better.