The mechanism of synergism for mixtures of phase-transfer carriers QD with tertiary amines and pyridine in the epoxidation reaction of allyl chloride has been established. It has been shown that tertiary amines (triethylamine, tributylamine, N,N-dimethylaniline, and N-methyldiethanolamine) and pyridine oxidizable in situ to N-oxides promote the transfer of the organic substrate (allyl chloride) to the interface (PB). It is assumed that the synergism of mixtures of phase-transfer carriers QD with a tertiary amine oxide or pyridine oxide can also be due to the formation of a mixture of two catalysts, Q(3)[PW4O24] and WO(O-2)(2)L (where L = a tertiary amine oxide or pyridine oxide). The WO(O-2)(2)L complex will provide the stage of reoxidation of the complex Q(3)[PW4O24 - (N...) ] in the organic phase and, hence, the possibility for the development of the process of epoxidation not only at the interface but also in the bulk of the organic phase. The maximum coefficient of synergistic effect (k (s) = 2) is observed for a mixture of cetylpyridinium bromide (90 mol %) and pyridine N-oxide (10 mol %).