Oil prices are very volatile. But much of this volatility seems to reflect short-term, transitory factors that may have little or no influence on the price in the long run. Many major investment decisions should be guided by a model of the long-term price of oil and its dynamics. Data on futures...

In a short sale, an investor sells a share of stock he does not own and profits when the price of the stock declines. A peculiar feature of short sales is the apparent increase in the number of shares of stock beneficially held by investors over and above the actual number of shares issued by...