I'm not sure we're really talking apples and apples here. In the area of oil, the people who sell directly to the consumer (us) are the same people who produce the product. In the case of corn, that isn't true. The farmers may all sell to the boards at the same price, but if I go to various supermarkets or vegetable markets, I will find small variances in the price of corn because they compete for busness through quality and/or price.

If I go to various retailers (service stations) to fill my car's tank, I don't find such competition between the sellers.

>In a sense they do - it is market driven:
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>http://www.dailygazette.com/news/2008/feb/17/0217_Corn/
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>>If every corn producer sells at exactly the same price and there is no semblance of competition, then yes, I'd call them a cartel too - especially if their prices just happened to change all at the same time. Trying to pretend that prices at the pump just coincidentally rise by the same amount at the same time for all the companies is simply laughable. Cartels are illegal in the U.S. and Canada, and it is very disappointing that they are tolerated by our governments. I know that speculators are getting a lot of return on their investments, but that is not a good argument for allowing this sort of activity.