The dispersibility of soot in a lubricant formulation containing a dispersant is evaluated by (a) preparing a dispersion of carbon black in the lubricant formulation; (b) depositing a sample of the dispersed carbon black from step (a) onto a planar chromatography medium; (c) subjecting the sample of (b) to chromatographic conditions and (d) evaluating the extent of migration of the carbon black by comparing the density of darkening due to carbon black at pre-defined locations along the chromatography medium. The liquid mobile chromatography phase comprises a mixture of a liquid non-aromatic hydrocarbon portion having viscosity and boiling point less than that of an oil of lubricating viscosity; and an oil component comprising an oil of lubricating viscosity and the dispersant or dispersants that are also contained within the lubricant formulation.