[MADN3SS]

Some info on "summer blend".

The expected increase in gas prices this summer has been partly blamed on the use of "summer blend" gasoline. What is "summer blend," and why is it making gas expensive?

To protect the ozone, the U.S. Environmental Protection Agency mandates that a special type of gasoline be used during the summer in certain parts of the country.

From June 1 to Sept. 15, gas stations are required to sell gasoline that produces lower emissions, which is more expensive than regular gasoline.

This year, there's an extra wrinkle because petroleum refiners and retailers are phasing out use of an additive that injects oxygen into gasoline and results in cleaner burning and less tailpipe pollution.

The additive -- methyl tertiary butyl ether, or MTBE -- is banned in some states. Petroleum refiners are using corn-based ethanol instead. Ethanol is common in the Midwest, but is in short supply in the South and on the coasts.