New York Mercantile Exchange futures prices actually go out 8 years, and show little decline during that period. As my colleague John Nye suggested this morning, though, a flat nominal price for 8 years with 3% inflation implies a 20% fall in the real price. I'll need a bit more to win my bet with Tyler and David Balan, but I'm not too worried.
Note further: The volume for the long-term future contracts is extremely low. That hardly shows that the market price is an overestimate, but it should reduce confidence in its accuracy. Any idea what the transactions costs for short-selling such a thinly-traded item are?