The city of Boston won a major property tax dispute at the Appellate Tax Board last month over how to value property owned by the city’s gas utility, particularly miles and miles of underground pipes.

The decision, issued on Dec. 16, could influence how other cities and towns across the state value gas and other utility property.

While the outcome of the ATB decision, pending any appeals, would not lead to an increase in the tax levy in any municipality that uses a Boston-type valuation methodology, it would increase the size of the local tax base and thus result in lower tax bills for other business and residential taxpayers.

The tax dispute arose over the valuation methodology used by Boston to calculate property tax bills in fiscal 2004 for both real and personal property owned by Boston Gas Company (now part of National Grid). Boston Gas sought tax abatements from the ATB through fiscal 2009.

The city used a combination of the traditional “net book value” method for determining value and a method designed to capture any fair market value of the property above the book value. The Boston Gas argument, as summarized in the ATB decision, is that the “fair market value of rate-regulated utility property is limited to its net book value.”

Boston assessors argued that because of changes in regulatory policy and laws and what has happened in the marketplace for utility property, “the fair market value of the real and personal property at issue in these appeals exceeds its net book value.” In denying the abatement petition, the ATB found that Boston Gas did not demonstrate that the fair cash value of the property was limited to net book value.

According to the ATB report, Boston Gas in 2002 provided service to 575,000 customers in 81 cities and towns through “a 6,200-mile network of pipe, storage facilities and associated equipment.”

The ATB decision marks an important defense of the property tax base against legal and statutory attempts to restrict property values or to exempt property from local taxation.