It's possible those cheaper stations were taking a loss at their original price points.
Margins at the store level *are* very low on gasoline.
"An industry group says an average of one in every 1,100 gasoline fill-ups last year was a gas theft. With about one cent per 1 gallon as profit, a retailer would have to sell an extra 3,000 gallons to offset each $30 stolen."
I won't quote the whole article, but it's worth a quick read.
http://slate.msn.com/id/2100546/
One salient point is that the price for 'oil' or oil futures can change by the minute, the price the retailer pays can change every couple days when he fills up, but he tries to avoid changing his price at the pump minute-by-minute. So the gas he bought for 2.00.gallon on Monday, he sells it for 2.10 or 2.20/gallon till he buys more on Wednesday -- 5 or 10% markup. When he buys gas on Wed, he now pays 2.40/gallon--they generally won't go from 2.10 to 2.60 in one jump. So he moves to 2.30 or 2.40, which means his markup is negative or nil, until he can make that next step to 2.60. So at any given time he might be 'making' 25 cents/gallon markup, but that 25 cents helps him recover from when he only had a 2 cent markup.
[all dollar amounts are made up, this is an example.]
"In 2003, convenience store owners reported an 8.8 percent mark-up* on gas, meaning if gas cost them $1.00 per gallon, they could sell it for $1.088. That's the lowest mark-up since 1985, according to the National Association of Convenience Stores. Add in credit-card fees—typically 3 percent—and the cost of distribution, which ranges between 2 and 4 percent, and the margins for gas are razor-thin, at the most a couple of pennies on the dollar"
http://slate.msn.com/id/2100546/
Couple other interesting articles about gas stations/behind the scenes:
http://www.startupjournal.com/runbusiness/survival/20050531-herrick.html
Credit cards are another big factor, like these articles say. VISA and MC charge a fee for every transaction, which can make a big difference.
http://www.detnews.com/2005/commuting/0505/12/C01-169772.htm
Of course, human psychology comes into play as well:
"Jeanette Burke of Oak Park said she, too, likes the idea of a discount for paying in cash. But she would feel differently if a station just raised the price for customers who use credit. [um...the end result is the same]
"I don't think that's fair," said Burke, 38. "Why should they charge one price to one customer and another price to someone else?" " [They aren't charging different customers different prices--they are charging different *payment methods* different prices. Lots of industries do this--my Domino's wants 20 cents for writing a check; I pay an additional fee to pay my insurance with a check every two months instead of an EFT every month, etc].