Abstract In order to use particle-in-cell (PIC) simulation codes for modeling collisional plasmas and self-sustained discharges, it is necessary to add interactions between charged and neutral particles. In conventional Monte Carlo schemes the time or distance between collisions for each particle is calculated using random numbers. This procedure allows for efficient algorithms but is not compatible with PIC simulations where the charged particle trajectories are all integrated simultaneously in time. A Monte Carlo collision (MCC) package including the null collision method has been developed, as an addition to the usual PIC charged particle scheme which will be discussed here. We will also present results from simulations of argon and oxygen discharges, and compare our argon simulation results with experimental measurements.