THEME: OIL

Refining is hardly a model of pure competition. A merger wave has left ownership highly concentrated, and the big players know that any large increase in their output would push down prices and shrink profits. According to an analysis of corporate filings by Public Citizen's Energy Program, a liberal research group, the top five refiners controlled 51% of domestic capacity last year, while the top 10 controlled 77%. That's a sharp increase from 10 years earlier, when the top five had just 33% and the top 10 had 54%.