The NYT has an article looking at the economics of oil refining in the United States. A sample: "Refineries, especially smaller ones, have been closing for many years. The number of refineries in the United States fell to about 150 in recent years from more than 300 in 1982. At the same time, the nation’s refining capacity grew by about 13 percent, as companies expanded their most efficient refineries."
[Update: The Houston Chronicle has a related article on the possibility that some refineries will be sold to foreign companies.]