The photochemistry of ketene has been studied at 3130, 3340, and 3660 Å. Quantum yields for carbon monoxide, ethylene, ethane, and acetylene were measured versus pressure. As p→0 the carbon monoxide quantum yield approaches 2 at each of the three wavelengths. Ethane and acetylene exhibit linear Stern-Volmer plots at 3130 and 3340 Å. However, at 3660 Å no acetylene was detected and ethane is formed in trace amounts. The above measurements are interpreted in terms of a mechanism which involves adduct formation between the 1A1, and 1A 2(1A″) electronic states of ketene.