Requiring retailers in seven southern and central Maine counties to sell a cleaner-burning gasoline could reduce two types of smog-causing emissions by about 6 percent and 1 percent a year, according to rough estimates provided by the state to federal regulators.

But industry analysts and the Maine Department of Environmental Protection, which is perusing the new rule, differ on whether the new fuel will cost more at the pumps.

The DEP is asking the U.S. Department of Environmental Protection Agency to allow the state to rejoin its reformulated gas program.

The DEP has estimated that volatile organic compound emissions and nitrogen oxide, which contribute to air pollution, could be reduced by 123 tons, or 6 percent, and 28 tons, or 1 percent, respectively.

Maine opted out of the program in 1998 because of an additive to the reformulated fuel, MBTE, was contaminating well water.

Now that MTBE no longer is used in reformulated gas and supply chains for the fuel have matured, Maine is looking to re-enter the program so it can better meet requirements under the Clean Air Act, according to the DEP testimony before a Legislative Committee in 2013.

Amendments to the Clean Air Act in 1990 sought to reduce high ozone areas, primarily along the northeast coast — roughly from Maryland to New Hampshire — and in California.

According to the EPA, as of April 2012, counties in 13 states, where smog levels are high, were required to use reformulated gas. Counties in 13 other states have opted into the program. Several counties in Maine, New York and Pennsylvania, opted out of the federal reformulated gas program.

Only seven Maine counties — York, Cumberland, Sagadahoc, Androscoggin, Kennebec, Lincoln and Knox — are subject to Clean Air Act’s fuel standards. Those counties are allowed to sell only a reformulated, cleaner burning fuel from May 1 to Sept. 15. The rest of the year, conventional gas, which is not as clean because it contains higher levels of butane but is cheaper to produce, can be sold.

The remainder of the state, which is not subject to the stricter standards, can sell the conventional gas year-round.

Jamie Py, the president and CEO of the Maine Energy Marketers Association, said the boutique gas, which according to the DEP is used in only five states, is refined in Europe whereas the cleaner-burning reformulated gas is refined in New York and Philadelphia.

“We’re already producing up and down the East Coast,” Py said.

Py said it makes sense for the same fuel to be sold, not only regionally among the communities that are subject to the EPA rules, but also for the entire state. Such a move would level the playing field for gas retailers, especially those along the borders that are forced to pay a higher price for gas, he said.

Py stressed that the reformulated gas performs as well as — and does not contain any more ethanol as — the current gas stock. Analysts say it is difficult to predict how the switch will affect the price at the pump.

Gas prices are determined by a complex set of circumstances, including the price of crude oil and the cost of additives, as well as efficiencies — or the lack thereof — in the refining process and supply chain.

The state and local gas retailers think the reformulated gas would cost the same as, if not less than, the gas currently being used, but industry analysts at GasBuddy.com said the reformulated gas has cost more this summer.

GasBuddy.com’s Chief Oil Analyst Tom Kloza said that from June throughout most of August reformulated gas cost 7 to 10 cents a gallon more than the boutique gas being used in southern and central Maine. That price difference is attributed to a lack of availability in offshore markets and the fact that it’s difficult to produce here in the summer, he said.

Patrick DeHaan, a senior petroleum analyst for GasBuddy.com, said gas prices vary for a variety of reasons. “You may get slightly better fuel efficiency,” DeHaan added, estimating that drivers could get an extra mile per gallon since reformulated gas evaporates more slowly than conventional and boutique gases.

In April 2013, Marc Cone, the director of the DEP’s Bureau of Air Quality, told the Environmental and Natural Resources Committee that the reformulated gas would be less expensive than the boutique gas currently used, according to committee documents.

“The Department believes this proposal will likely decrease the costs of gasoline while meeting the federal Clean Air Act requirements, reduce the need to impose additional regulatory burdens on industry and improve the air quality for people in Maine,” Cone said. “This would result in a win for retailers and consumers in the state.”

John Babb, president of J&S Oil, told the committee in 2013 that at times the boutique gasoline costs as much as 15 cents a gallon more than the gas used by competitors in counties not under the EPA mandate.

“The burden is especially sharp for county border stores … who consistently pay a higher cost for the product and often have to sell it below cost to maintain a competitive price with other stores that are often only a couple miles away,” Babb said.

Motorists gassing up Friday at the Irving station on Commercial Street in Portland mostly said they wouldn’t mind paying a little bit more for gas to protect the environment, as long as it didn’t reduce the performance of their vehicles.

“I’d pay more for better quality,” said Cathy Flint, who was driving a 1965 Rambler Classic 550. “If it’s better all the way around, of course.”

Others said there was a limit on how much extra they’d pay.

“It depends how much we’re talking,” said Dana Carter, a Scarborough resident driving a Silverado work pickup. “Fifteen cents wouldn’t bother me.”

“To a certain degree, I would like to help the environment, but not if it increases the price by 10 or 15 percent,” said Kerry Dineen, a Biddeford resident who drives a 2001 Mercury Cougar. “I have a hard time getting by as it is.”

Erik Henderson, however, said prices need to be kept as low as possible, because when gas prices go up, so do the prices of other goods, such as milk and bread. “The cheaper the better,” he said.