Emulsified acids were traditionally used in acid fracturing, and more recently on matrix treatments of carbonate formations. The delayed nature of emulsified acids is useful in generating longer etched fractures or deeper wormholes. Emulsified acids also have higher viscosities than straight acid, which reduces fluid loss in acid fracturing applications and helps distribute acid more uniformly in formations with high-permeability contrast during matrix treatments. A new emulsified acid system is presented in this paper that is stable up to 350 F, highly retarded, and significantly more viscous than straight acid. Laboratory data comparing emulsified acid with straight acid are presented at temperatures ranging up to 350 F, including rheology and acid conductivity. Field case histories in the Smackover formation in Alabama over two years are presented. The field case histories show the improvements in production of oil and gas resulting from emulsified acid fracturing treatments in comparison with prior similar treatments done with straight acid.