Economists note there should not be two prices for one thing at the same place and time. Could a drugstore sell two identical tubes of toothpaste, and charge 50 cents more for one of them? Of course not.

But, in effect, exactly that has been happening, repeatedly and mysteriously, in trading that sets prices for corn, soybeans and wheat — three of America’s biggest crops and, lately, popular targets for investors pouring into the volatile commodities market. Economists who have been studying this phenomenon say they are at a loss to explain it.

Whatever the reason, the price for a bushel of grain set in the derivatives markets has been substantially higher than the simultaneous price in the cash market.

These disparities also raise the question of whether American farmers, who rely almost exclusively on the cash market, are being shortchanged by cash prices that are lower than they should be.

[Read](http://www.nytimes.com/2008/03/28/business/28commodities.html?ex=1364356800&en=090041d284408c21&ei=5088&partner=rssnyt&emc=rss “Read the Article”) (New York Times)