A united-atom force field for ethylene oxide (oxirane) is presented. Parameters for both the dispersive and electrostatic interactions are simultaneously determined by fitting to the experimentally determined critical point, the normal boiling point and two vapor pressures. Vapor and liquid coexistence densities, heats of vaporization and vapor pressures are determined with histogram-reweighting Monte Carlo simulations in the grand canonical ensemble. NpT simulations are used to determine the heat capacity and isothermal compressibility.