Richir Sharma argues that commodity prices always go down in the long run because of "new technologies, greater efficiency in extraction and the substitution of one commodity for another":
At some point, of course, commodities will spike again, but only temporarily. To date, the centuries-old slide in prices has been marked by long bear markets and short bull runs. Data from CSFB shows that the average bull market in oil has lasted from four to nine years, and the average bear market from 11 to 27 years. The bull market that ended last summer saw prices rise tenfold over nine years, mirroring the duration and magnitude of the previous bull market, which ended in 1979 (see chart above). That was followed by a bear market that lasted 20 years. If history is any guide, we're only at the beginning of another long one.
One of Mark Perry's commenters counters.