Zone pricing articles from a quick Google:

Reprint of WSJ article from 2000 (with BB comments)
4/2/04 article from a Palm Springs, CA paper
CBS News coverage from 2003

Especially note this line from the CBS article:
Quote:

"Zone pricing is basically a demographic study of the income, the competition in that area and they determine what they can extract in that given market area," says DaCota.



DaCota is a station owner in California. He hits it on the head with the "determine what they can extract" statement - oil companies charge as much as they possibly can wherever they can. "Who cares if consumers don't want to pay $2 per gallon? If we charge it, they have to pay it or walk."