Downeast Energy, one of the state’s largest oil dealers, was sold to an Oklahoma energy company today.

NGL Energy Partners LP said it agreed to acquire the Maine and New Hampshire offices of Brunswick-based Downeast Energy, which has been family owned for more than 80 years, for a combination of cash and partial ownership in NGL.

The deal marks the second sale of a Maine energy business this year. In January, Dead River Co of Portland agreed to buy Bangor-based Webber Energy Fuels’ retail heating oil business.

The exact terms of the deal were not disclosed.

Downeast Energy employs roughly 300 workers and serves 50,000 customers in New England. It has 14 offices in southern and central Maine, as well as Dover, New Hampshire.

The company has been owned by the Morrell family, which will no longer  be active in day-to-day operations of the company.

The Morrell family said it was with “mixed emotions” that it made the announcement. “We want to thank you for all the years we’ve been able to be of service and to assure you that you will remain in excellent hands,” the family said in a letter to customers on the Downeast Energy Facebook page.

“One of the major benefits of this partnership provides us access to more reliable fuel supplies. Concurrent with Downeast joining the NGL partnership, we will be opening a supply terminal in Portland,” Downeast said.

John Peters, Downeast’s president, will remain with the company. NGL Energy operates midstream, wholesale suppy and marketing and retail propane businesses.

Correction: This story was revised at 1:53 p.m., April 23, 2012, to correctly reflect the total number of workers at Downeast Energy. It employs roughly 300 people.