The utility will have a market capitalization of approximately $7.8 billion, based on each company’s closing stock price as of Monday.

Black Hills Energy and NorthWestern Energy officials announced Tuesday that the two South Dakota-based companies plan to combine in an all-stock, tax-free merger.

NorthWestern Energy Group and Black Hills have agreed to combine to form a large $7.8 billion regulated electric and natural gas utility company at a time of climbing energy demand across the U.S.