A numerical model is presented to study the effects of surfactants on liquid droplets in air at intermediate Reynolds numbers. The model uses the Gibbs surface equation of state to relate surface tension to surfactant concentration. The strongly coupled surfactant transport equation and the gas and liquid-phase momentum equations are solved simultaneously without making any assumptions concerning the form of the droplet surface velocity distribution. The numerical model is validated against exact analytical result for droplets in creeping flows. A steady-state study performed at a Reynolds number of 100 examines the effects of surface-tension-related parameters on droplet drag, and interface velocities.