PORTLAND – Low-income Mainers who receive government subsidized heating assistance aren’t necessarily getting the best deal for fuel they buy, says a Portland agency that monitors prices.

Energy Data Corp. says the Massachusetts fuel assistance program forces oil dealers to sell below retail rates, which in effect enables subsidy recipients to put more fuel in their tanks.

But Maine’s Low Income Home Energy Assistance Program, known as LIHEAP, allows qualified low-income customers to choose their oil dealers and pay prevailing cash prices. The state expects to assist about 50,000 households this heating season.

According to an analysis by Energy Data, 40 percent of the nearly $17 million in LIHEAP money spent on oil and kerosene in Maine last heating season went to six big oil dealers that charged above-average prices.

In some markets, differences in prices charged by competing dealers can range up to 25 cents a gallon. Consumers could buy millions more gallons of fuel if the price they pay was knocked down by pennies a gallon.

“It’s hard to convince me that the most expensive fuel companies should get most of the money,” said Chris Brown, president of Energy Data.

LIHEAP is due to receive $19 million this winter. The money comes from the federal government and is managed by the state and distributed through the state’s network of community action agencies.

Spokesmen for state government and the oil industry say Energy Data’s analysis is too simplistic and doesn’t take certain factors into account.

Some small dealers with a few trucks and little overhead, for example, may offer cheaper prices but do not have burner service or 24-hour delivery in rural areas.

“It’s the difference between knowing the cost of something compared to knowing the value of it,” said Gene Guilford, executive director of the Maine Oil Dealers Association.

Energy Data’s analysis comes as northeastern states respond to a flood of LIHEAP applications. States are taking different approaches to stretching the fuel-subsidy dollars furthest.

New Hampshire is considering borrowing general fund money so clients can buy oil in the summer when it’s cheaper, then pay back the spending when LIHEAP money becomes available.

But New Hampshire has rejected ideas that would exclude small dealers or threaten existing dealer-customer relationships.

“In shopping for price, we don’t want to lose critical services,” said Mary Ann Manoogian, the Granite State’s assistant director for community services.

Massachusetts sets a 26-cent-per-gallon margin over the wholesale oil price, which gives dealers some profit, but less than they would get on the open market.

“Dealers will scream bloody murder,” said James Hays, director of the bureau of energy programs in Massachusetts. “But it’s something they’ll get used to.”