Regulators discovered late last year that southern Maine natural gas utility Maine Natural Gas had billed some of its largest customers 10 times less than it should have, raising concerns about impacts on the utility’s other customers.

The Maine Public Utilities Commission on Wednesday issued a notice that it has opened an investigation into the Maine Natural Gas underbilling, which the commission said ranged from 2002 to 2016 and affected 11 different large accounts for varying amounts of time.

Regulators said the problem stemmed from bad readings of the company’s meters for large customers. The meters could be set to display gas volumes in hundreds of cubic feet or thousands of cubic feet.

Typically, for smaller customers, those readings are in the smaller unit of measure. In some cases, the utility found readings were wrongly reported in hundreds of cubic feet, reducing that customer’s bill by a factor of 10. Regulators did not estimate how much the utility underbilled in total.

Maine Natural Gas, a subsidiary of Avangrid, which also owns Central Maine Power Co., serves customers in Gorham, Brunswick, Freeport, Topsham, Bowdoin, Gorham, Windham and Augusta.

The utility has since issued bills to customers seeking to recover those amounts, but regulatory rules limit it to recovering payments only for the past 12 months.

The utilities commission opened an investigation into the case out of concern that the extent of the underbilling would have affected other Maine Natural Gas customers in past cases to set the utility’s cost of gas and base service rates.

“It remains an open question whether further adjustments to cost of gas or other rates may be warranted to correct inequities to other customers,” the commission wrote in its notice issued Wednesday.

The commission said it will take petitions to intervene in the case until Sept. 11.

Darren Fishell

Darren is a Portland-based reporter for the Bangor Daily News writing about the Maine economy and business. He's interested in putting economic data in context and finding the stories behind the numbers.