Peak Oil unbelievers

I'm amazed to see people who spout "peak oil" and claim that oil will hit, say, $150/barrel 5 years from now. Well, if you look at the oil futures, you can buy oil futures of December 2011 for $67.61. That's 122% return in 5 years. So, why aren't these believers buying all those futures up? [Or did they already buy and, like penny stock promoters, trying sell for a higher price?]