“The commodity traders are arbitragers par excellence, trying to exploit a series of differences in prices. Because they’re doing deals to buy and to sell all the time, they are often indifferent to whether commodity prices overall go up or down. What matters to them is the price disparity – between different locations, different qualities or forms of a product, and different delivery dates. By exploiting these price differences, they help to make markets more efficient, directing resources to their highest value uses in response to price signals. They are, in the words of one academic, the visible manifestation of Adam Smith’s invisible hand.”