The viscous behaviour of suspensions of asphaltene nano-aggregates is often described in terms of the Pal and Rhodes model (Pal, Rhodes, J. Rheol. 1989, 33, 1021). The model assumes particles to be spherical in shape and takes into account the solvation or hydration of particles. However, the solvation coefficient estimated from the Pal and Rhodes model for asphaltene particles is generally too high to be realistic. Furthermore, the model does not consider the packing limitations (maximum packing volume fraction) of the asphaltene particles. A large body (14 sets) of the available viscosity data for asphaltene suspensions are reinterpreted in terms of the Krieger-Dougherty model. The data analysis indicates that asphaltene nano-aggregates are non-spherical disk-shaped particles with low aspect ratio (ratio of particle thickness to particles diameter). The aspect ratio depends on the nature of the asphaltene/oil system. For a given system, it increases with the increase in the temperature. Interestingly, the maximum packing volume fraction (phi(m)) of asphaltene particles is found to be nearly constant (phi m approximate to 0.37), independent of the nature of the asphaltene/oil system and temperature. Also the values of phi(m) predicted from the viscosity data are in reasonable agreement with the values predicted from a percolation model. Based on the analysis carried out in this work, the following model is proposed for accurate estimation and correlation of the viscosity of asphaltene suspensions: (r)=[1-(phi/0.37)](-0.37[]), where (r) is the relative viscosity, [] is the intrinsic viscosity and phi is the volume fraction of asphaltene particles.