Recently the surface state model of tribocharging has been used to determine the relative work functions of toners. The approach consists of examining the correlation between charge-to-mass data for a series of toners measured using several carriers of differing charging ability and the charge-to-mass of a reference toner measured using the same carriers. In this article this method has been used to analyze published data on the charging behavior of toners containing carbon blacks with different contact potentials. An excellent correlation was found between the relative work functions estimated from the triboelectric data and direct contact potential measurements. The results confirm that relative work functions of toners can be accurately estimated using the surface state model. The analysis also shows that in general these materials follow the high-density limit of the surface state model.