With all the excitement over Celsius lately, one could lose sight of the fact that global players Red Bull and Monster still control more than half the US energy drink category. Each is busily defending its turf while growing volume and dollars. But with long-standing or second-generation owners, they are ripe for M&A speculation.                   

Rumors last week that Red Bull co-founder Dietrich Mateschitz is seriously ill sparked just such talk. Dietrich and his family hold 49% of Red Bull. The family of the late co-founder Chaleo Yoovidhya owns the rest. Could the company...