On such long terms you allways better off looking at yields rather then prices, esp. unadjusted futures prices. Now, the yields have been coming off from the 80s, but so did inflation. Over the longer frame you will see that it's nothing more then reversion to mean.Quote from futures_shark:
I found an adjusted chart somewhere that showed a very strong uptrend that started in the 80's still going strong. You can imagine it if you look at the chart with the bad data and just subtract 20 points before 2000.