Arby’s operator Inspire Brands Inc. will acquire Sonic Corp. in a deal valued at about US$2.3 billion as the fast-food burger wars heat up.

Inspire, whose chains include Arby’s, Buffalo Wild Wings and Rusty Taco, will continue to operate Sonic as an independent brand, it said in a statement. The deal, which was unanimously approved by Sonic’s board, represents a 19 per cent per share premium to Sonic’s closing price on Monday, the company said. Inspire will assume Sonic’s net debt.

Sonic becomes the latest struggling restaurant chain to be acquired by Inspire, which is credited with mounting a turnaround at sandwich chain Arby’s. Sonic, squeezed by tough competition from larger rivals Burger King and McDonald’s Corp., has posted declining same-store sales for eight consecutive quarters. The chain relies on cheap drinks, catchy commercials and promotions to lure customers, and it’s struggled to stand out in a crowded restaurant space.

Inspire was co-founded by Paul Brown of Arby’s and Neal Aronson, who started Roark Capital Group. Last year, Roark agreed to buy restaurant chain Buffalo Wild Wings for about US$2.4 billion, adding it to the private equity firm’s stable of eateries. Last month, Wendy’s Co. agreed to sell its stake in Inspire, marking another ownership change in a rapidly shifting restaurant industry.

The transaction is still subject to the approval of Sonic shareholders.