This is known as "Zone Pricing" or "Geographical Pricing".

http://articles.latimes.com/2005/jun/19/business/fi-calprice19

Such price variations may seem odd, but they are not unique to Anaheim. On any given day, in any major U.S. city, a single brand of gasoline will sell for a wide range of prices even when the cost to make and deliver the fuel is the same.

 

The primary culprit is zone pricing, a secret and pervasive oil company strategy to boost profits by charging dealers different amounts for fuel based on traffic volume, station amenities, nearby household incomes, the strength of competitors and other factors.

 

It's a controversial strategy, but the courts have thus far deemed it legal, and the Federal Trade Commission recently said the effect on consumers was ambiguous because some customers got hurt by higher prices while others benefited from lower ones.

http://en.wikipedia.org/wiki/Geographical_pricing

Zone pricing, as practiced in the gasoline industry in the United States, is the pricing of gasoline based on a complex and secret weighting of factors, such as the number of competing stations, number of vehicles, average traffic flow, population density, and geographic characteristics. This can result in two branded gas stations only a few miles apart selling gasoline at a price differential of as much as $0.50 per gallon.

But the short answer is "because they can". It's legal, provided that some people are paying less while others are paying more. Essentially the larger, richer audience is subsidizing the product for other areas. It's not terribly different than the way most drugs are priced in the world.

This is known as "Zone Pricing" or "Geographical Pricing".

http://articles.latimes.com/2005/jun/19/business/fi-calprice19

Such price variations may seem odd, but they are not unique to Anaheim. On any given day, in any major U.S. city, a single brand of gasoline will sell for a wide range of prices even when the cost to make and deliver the fuel is the same.

The primary culprit is zone pricing, a secret and pervasive oil company strategy to boost profits by charging dealers different amounts for fuel based on traffic volume, station amenities, nearby household incomes, the strength of competitors and other factors.

It's a controversial strategy, but the courts have thus far deemed it legal, and the Federal Trade Commission recently said the effect on consumers was ambiguous because some customers got hurt by higher prices while others benefited from lower ones.

http://en.wikipedia.org/wiki/Geographical_pricing

Zone pricing, as practiced in the gasoline industry in the United States, is the pricing of gasoline based on a complex and secret weighting of factors, such as the number of competing stations, number of vehicles, average traffic flow, population density, and geographic characteristics. This can result in two branded gas stations only a few miles apart selling gasoline at a price differential of as much as $0.50 per gallon.

But the short answer is "because they can". It's legal, provided that some people are paying less while others are paying more. Essentially the larger, richer audience is subsidizing the product for other areas. It's not terribly different than the way most drugs are priced in the world.