With gasoline at $4.10 a gallon, why are gas stations closing in Rhode Island and why is ExxonMobil, one of the world’s energy giants, following the lead of its competitors and selling all 2,200 of its retail outlets in the United States?

It seems the people who pump gas should be making a killing.

But they are not.

In fact, gas station owners are struggling. Many independent owners are barely breaking even.

The reason is that the economic fuel chain rewards oil companies at the top that pump oil out of the ground and squeezes the little guys at the bottom that sell gasoline to motorists.

The result is that as gas prices have spiked, stand-alone stations are disappearing, just like the attendant who used to clean your windshield, check the oil, fill the tank and still be able to give you back change from a $10 bill.

In their place are more gas stations tied to convenience stores, sandwich shops and other retailers that want to sell you coffee, snacks and other goods while you fill up.

All the changes in the gas station business have been accelerated by the run-up in the price of oil and are based on the math of how crude pumped from the ground gets to your gas tank. Here’s how it works:

Crude oil sold last week for about $130 a barrel.

With 42 gallons per barrel, that sets the price at $3.10 a gallon.

But before it gets to your tank, it has to be transported from the oil fields to refineries, where it goes through a refining process that turns the crude into gasoline.

All that adds to the price per gallon. Then the gasoline has to be transported from the refinery to the terminal for distribution, usually by a wholesaler who sells it to the gas station owner.

On top of all those costs, there are state and federal taxes. In Rhode Island, it’s 31 cents on top of the 18.4 cents federal tax.

In 2007, the average markup of gas sold at the pump was 14.3 cents per gallon over what the owner paid, according to data from the National Association of Convenience Stores, the trade group for the stores that run more than 80 percent of the country’s gas stations.

The profit, or net margin after all expenses have been figured in, shrunk to about 1.5 cents a gallon.

That’s because the station owners’ costs have gone up, including the expense of transporting the gas to the stations.

And when it is pumped, more than two-thirds of purchasers are using credit cards to pay for gas rather than carrying wads of cash. Each time the plastic is swiped, credit card companies charge 2.5 to 3 percent of the total. So as the price rises, and more people pay with cards, station owners have to pay more to the credit card companies, cutting their take. For example, at $4.10 a gallon, a 2.5-percent fee equals 10.5 cents.

The station owners also have to pay overhead: wages, rent, electricity, depreciation and other costs of doing business. All that slices margins thinner.

On top of that, most station owners have to borrow money to pay for the inventory of gasoline to fill the underground tanks. As the cost of gasoline rises, borrowers have to extend their lines of credit, raising their liability and creating a cash flow crunch. It also leaves them less able to borrow for anything else.

This year, the markup has shrunk to 11 cents, further cutting the station owner’s profit margin. For many, it’s not enough to stay in business.

For example, if you pump 4,000 gallons a day and the profit is only 1.5 cents a gallon, the owner makes $60 a day on gas, hardly enough to run a business.

And because of competition, station owners can’t just raise prices to boost their margins. Most motorists now look for the best price, not the brand or the location. They’ll pass by one station to find another with cheaper gas.

“Gasoline has never been higher, but it’s never been harder for the station owner to make a living,” said Jeff Lenard, vice president of communications for the convenience store association.

Nationally, the number of fuel distributors has shrunk from 202,000 in 1994 to 164,000 in 2007, according to the National Petroleum News. In Rhode Island, the number has fallen from 545 in 1994 to 377 last year.

ExxonMobil, the world’s largest publicly traded oil company, said it plans to sell all its retail outlets. Other companies unloading low-profit retail gasoline businesses are BP Plc and ConocoPhillips. Some large wholesalers are expected to bid on the stations for sale.

“It continues to be a very challenging market with reduced margins,” explained Exxon spokeswoman Premlata Nair.

The economics of gasoline pricing has changed the retailers who sell gas.

To widen margins, gas station owners also want customers to buy food, snacks, drinks and other items. Some stations are co-branding their stores with Dunkin’ Donuts, Subway sandwich shops or grocery stores. Some of the bigger retailers, such as BJ’s Wholesale Club, Costco, and WalMart Stores have built gas stations in their parking lots and have become major players in the gasoline business.

Sometimes, it’s easy to get angry at the guy climbing the ladder at a service station to raise the price, again, or the clerk behind the counter who takes your money. But the owner of the station isn’t the reason that motorists are paying record prices for gasoline.

If you want to point the finger at someone, consider that Exxon Mobil reported sales of $404 billion last year and profits of $40.6 billion, a record. Those net earnings are among the $123 billion collected by the major oil companies last year.

The problem is at the start of the chain, not at the end where you fill your tank.

jkostrze@projo.com