The invention is a method of assessing at least one petroleum characteristic of a rock sample. Starting from a temperature ranging between 50° C. and 120° C., the temperature of a rock sample is raised to a temperature ranging between 180° C. and 220° C. which is maintained for a predetermined time duration. The temperature of the sample is increased to a temperature ranging between 330° C. and 370° C. which is maintained for a predetermined time duration. The temperature of the sample is then raised to a temperature ranging between 630° C. and 670° C. Three quantities representative of the amount of hydrocarbon compounds released during the temperature change stages are measured and at least one petroleum characteristic of the sample is deduced from these quantities.