It is not easy being green, particularly when gas is cheap.

With American drivers deep in the throes of SUV fever, Toyota's Prius, the standard-bearer of auto efficiency for almost 20 years, is in trouble. Not only are sales plummeting, but the little hybrid is losing market share among green vehicles as Tesla ramps up production and more mainstream brands crank out hybrids.

As Toyota sees it, the solution is sex appeal. Starting with a commercial in Sunday's Super Bowl, the Japanese giant is launching a massive marketing campaign to convince American drivers that the Prius is stylish and sporty, not just efficient and responsible.