Dominion Energy on Wednesday it would buy Scana in an all-stock deal that values the electric utility company at about $7.9 billion.

Scana's shares surged 27 percent in premarket trading on news of the deal.

Scana shareholders will receive 0.6690 shares of Dominion Energy for each share held, or the equivalent of about $55.35, the companies said.

The offer represents a premium of 42.4 percent to Scana's Tuesday closing price of $38.87.

—CNBC contributed to this report.