The kinetics of the singlet oxygen oxidation of diethyl sulfide in the presence of diphenyl sulfoxide and diphenyl sulfide in various sovlents (methanol, benzene and acetonitrile) were investigated. Competitive trapping of a single intermediate species by diethyl sulfide, diphenyl sulfide and diphenyl sulfoxide occurs in protic solvent (methanol), while in aprotic solvents (benzene, actonitrile) only diphenyl sulfide competes with diethyl sulfide. Diphenyl sulfoxide traps an earlier intermediate; the same intermediate also leads to quenching. A mechanism is proposed in which an initial nucleophilic intermediate can be trapped by electrophiles (diphenyl sulfoxide), lose singlet oxygen, or colapse to an electrophilic intermediate that can be trapped by sulfide nucleophioles. [These rsults are of interest to studies of the photosensitized deactivation of some enzymes.].