Houston-based power utility Spark Energy Inc. has agreed to purchase Electricity Maine parent company Provider Power LLC of Auburn for $28 million.

Spark Energy disclosed the purchase agreement in its quarterly earnings statement, filed Wednesday with the U.S. Securities and Exchange Commission. Provider Power is the parent of Electricity Maine LLC, Electricity N.H. LLC and Provider Power Mass LLC, all of which it has agreed to purchase.

Founded in 2011, Provider Power was the first “competitive provider” in Maine to really go after the residential market, more than a decade after Maine restructured its electric industry to encourage retail competition to the state-regulated Central Maine Power Co.

Prior to the founding of Provider Power, a vibrant market had developed in the commercial and industrial sectors, but the high cost of attracting and retaining residential customers and small business had been viewed as a turn-off for national energy suppliers.

According to Spark Energy’s financial statement, Provider Power has about 125,000 customers, mostly in Maine and New Hampshire.

Maine Public Advocate Timothy Schneider said most of Provider Power’s customers have defined contracts that determine the rates they pay for electricity. Those contracts would remain valid under Spark Energy’s ownership if the planned sale is completed, he said.

In other words, the sale isn’t likely to change the amount paid by customers of Electricity Maine or Provider Power’s other subsidiaries, Schneider said.

“We would expect that the new owner would honor those contracts,” he said.

Provider Power owners Kevin Dean and Emile Clavet could not be reached for comment Friday.

According to Spark Energy’s earnings statement, a portion of the $28 million purchase price would be payable at closing, and the remainder would be paid in 10 equal monthly installments starting on Aug. 1 and ending on May 1, 2017.

Spark Energy also has agreed to pay up to an additional $4 million if certain customer growth criteria are met by June 30, 2017, according to the statement.

Schneider said competitive providers such as Provider Power are not regulated by the state, which means the proposed sale would not require Maine regulators’ approval.