A mathematical model was developed on the basis of population balance to analyze experimental data on asphaltene floc size distribution in a coagulating suspension. Experiments were carried out in a Couette device under a laminar flow condition. Floc size distributions were measured on-line using optical microscopy and image analysis. The aggregation behavior of asphaltenes was investigated by monitoring the size distribution of flocs for various intensities of agitation (i.e., shear rate, G), solvent composition (i.e., ratio of toluene to n-heptane in the solution, T:H) and particle contents (i.e., volume fraction of particles, phi). The results showed that (i) the floc size distribution can be predicted using a population balance approach, (ii) a steady-state mean floc size is reached for a given shear rate, and (iii) this steady-state floc size increases as phi is increased or T:H is reduced. The relative rates of shear-induced aggregation and fragmentation determine the steady-state size distribution. Similar floc size distributions were obtained at steady state for various shear rates, indicating that the width of the size distribution is independent of shear. However, the experimental observations indicate that the steady-state floc size distribution depends on asphaltene concentration and solvent composition. (C) 2003 Elsevier Ltd. All rights reserved.