Evaluating the dispersive power of an oil for gasoline engines is included in international specifications such as the ones issued by the Committee of Common Market automobile Constructors (CCMC) and the American Petroleum Institute (API). This evaluation is the result of lengthy, severe and costly testing in engines on a test bench. These tests are performed in Mercedes M102E (CCMC levels G4 and G5) and Ford Pinto 2.31 (API levels SG and SH) engines. The cost of these tests requires the laboratory use of reliable preselection tests. The more often used test for evaluating the dispersive power of a motor oil is the ＇＇spot＇＇ test. It is performed in the presence of pollutants coming from an used Diesel motor oil (Tables 1 and 4, Fig. 2). However, some additive technologies that give good results for this test give poor results during engine testing (Table 2). During the VE Sequence lasting for 288 hr, the oil is subjected to different temperature cycles (Table 3). If the ＇＇spot＇＇ test is used to follow the evolution of the dispersive power of this oil as a function of testing time, curves shown in Fig. 1 are plotted. The OXYDISP and POTDISP methods proposed in this article can be used to obtain the same evolution and classification of products as during engine testing. These methods are based on the association of two successive sequences. The first sequence consists in the prior ageing of the lubricant by artificial oxidation at high temperature (160 degrees C or 180 degrees C) (Table 5). The second sequence corresponds to the evaluation of the lubricant dispersive power during and at the end of oxidation, using ＇＇spot＇＇ tests. The oxidized oil is then subjected to a specific treatment by artificial pollution at 200 degrees C, by means of sludge coming from an oil that had already been aged in a Ford Pinto 2.31 engine and water (Tables 4 and 6, Fig. 3). The ＇＇Residual Dispersive Rating＇＇ (RDR) curve is then plotted as a function of oxidation time (Figs. 5 and 12). This curve has the same configuration as the one described in the VE Sequence (Fig. 1). The plot of the RDR curves as a function of the Average Engine Sludge deposit (AES) is used to make a clear distinction between good and poor oils in the VE Sequence. After 96 h of oxidation for the OXYDISP test (Fig. 9) and 48 h for the POTDISP test (Fig. 14), we are in the presence of two families of products, i.e. products that preserve their RDR and obtain a ＇＇sludge＇＇ rating equal to or higher than 9 in the VE Sequence, and products that lose their RDR and that all have ratings lower than 9 in the same sequence. The OXYDISP and POTDISP methods can also differentiate oils having different API levels (levels SE, SF and SG) (Figs. 16 and 17).