The formation of colloid aggregates was monitored by measuring flocculation points of solutions of crude oils and oil fractions. With regard to concentration, flocculation points of crude oil solutions can be calculated analogous to flocculation points of polymer solutions. As criterion for the metastability of colloidal crude oil systems the Flory-Huggins interaction parameter can be used. The interaction parameter depends on the difference of solubility parameters between the surface of the colloid particles and the dispersion medium fraction of the oil. The critical interaction parameter of flocculation was found to be chi(crit) = 0.62 +/- 0.04.