Caseys General Stores, Inc. (CASY)

Fuel brings people in but earns almost nothing: the mark-up per litre is small and swings with the wholesale price. The money is made inside — on freshly prepared food, drinks and small items where the mark-up is several times higher. The company ranks among the country's largest pizza makers while remaining a chain of filling stations.

Location is the main barrier: in a town of a few thousand there is one site for such a shop, and whoever takes it captures nearly all the traffic. Growth comes from buying family-owned chains and converting them to the in-house kitchen. Risks: fuel prices, labour costs and the health of the rural economy. The company pays a small dividend and raises it annually.