The motion of solid particulates through flighted, horizontal rotating cylinders is important in governing the outcome of a number of particulate processes. In particular this phenomenon controls the residence time of the particles in the system. A model of particle kinetics must include the influence of the many random effects that are present so that the wide dispersion in residence time is accounted for. This paper decomposes the motion of the particles into two separate modes; transition from flight to flight simultaneously accompanied by axial motion through the drum. Particle motion between flights is analysed as a binomial random walk and motion along the drum as a trinomial random walk. A scheme is presented to couple both modes together so theoretical estimates of mean and variance in residence time can be found. The approach is validated by comparison with experimental measurements and numerical Monte Carlo simulations. (C) 2011 Elsevier B.V. All rights reserved.