SAUGUS – Heating oil company owners are thinking globally and smiling along with their local customers as prices continue to drop, shaving more than a dollar to date off the per-gallon cost for heating a home.?It hasn?t been this cheap in five years,” said Sarah Marchetti, who works for Saugus-based Angelo?s Oil.Angelo?s, John?s Oil in Lynn and Absolute Oil in Peabody were all charging well under $3 a gallon for oil Monday compared to heating oil prices as high as $4.90 per gallon a year ago. The state Executive Office of Energy and Environmental Affairs posted heating oil prices for a week ago on its website Monday, listing $3.10 as an average per-gallon price and a low price of $2.37, based on telephone surveys with full-service oil dealers.Oil prices that climbed in the first three months of 2013 are dropping so fast this year that John?s Oil?s Laurie Walsh said some customers have to rewrite checks after initially filling them out to pay for an oil order.?One guy told my driver, ?I was so used to writing three hundred-something,?” Walsh said.John?s has three drivers delivering oil in the Lynn area while nine Angelo?s employees include drivers delivering in Lynn, Saugus, Peabody and 12 other communities.Walsh, Marchetti and Absolute Oil Company owner Chuck Holden said theories vary on why oil prices are dropping, but most converge around strong U.S. oil production.?The bottom has fallen out of the international market: There?s more than an ample supply,” Holden said.Walsh?s husband, John, said falling prices are a pleasant byproduct of years, even decades of American oil expansion that includes exploitation of land-based oil sites and deep drilling in the Gulf of Mexico.?We?ve found a lot more oil and we are producing,” he said.The response to U.S. production by other oil-producing countries and weak demand for oil in Europe also translates into falling prices, local owners said. Walsh?s son, Joshua, doubles as delivery driver and oil price checker, balancing a delivery hose in one hand and a laptop in the other as he checks daily on oil prices.?We buy on the open market every day,” John Walsh said.Walsh is convinced oil prices will stay under three dollars a gallon. Holden is not so sure but he is glad he did not join other delivery companies a year ago in locking in per-gallon prices out of fear they would rise.Delivery companies build a margin into the per-gallon price for oil to cover payroll, utilities, credit card fees and other costs. The margin does not change, but Walsh and other owners said falling oil prices prompt customers to buy more oil and smile more.?Customers are nicer when it?s cheap,” Marchetti said.