An easy-to-implement solid/liquid extraction method has been developed to extract the basic molecules from petroleum crude oil in significant amounts (700−800 mg). The basic molecules are first extracted from crude oil using a cation-exchange sorbent, then recovered using methylamine. After checking the quantitativity of the method with model systems composed of commercially available basic and nonbasic molecules, four different crude oils spanning different properties (from light oil to extra-heavy crude oils) were tested. The efficiency of the method has been checked by determining the extraction yield from elemental analysis and titration measurements (total base number determination). Results show that 80−90% of bases are extracted from crude oils having densities comprised between 0.875 and 0.939 g.cm−3 at 15 °C. The extraction yield is significantly lower for an extra-heavy crude oil (around 70%).