A homogeneous binary catalyst system, n-BU4NBr/n-BU3N, was found to be active for the synthesis of dimethyl carbonate from styrene oxide (SO), methanol, and supercritical CO2. Under the optimized conditions, the dimethyl carbonate yield could reach 84% at SO conversion of 98%. Several parameters were studied, i.e. catalyst precursors, reaction time and temperature, methanol/epoxide feed ratio in moles, and CO2 pressure. The best compromise for the one-pot synthesis was achieved with an equimolar amount of n-BU4Br/n-Bu3N. A possible mechanism for the present n-BU4NBr/Bu3N-catalyzed one-pot synthesis of dimethyl carbonate was proposed. (c) 2005 Elsevier B.V. All rights reserved.