The performance of lubricant oils and, consequently, the performance of the engine and its useful life are significantly affected by the degree of contamination with fuel such as gasoline and ethanol. The determination of such contamination is of utmost importance both during the development of the engine components and for field verification. The official existing method is ASTM D3525, which is based on gas chromatography and requires significant investments in equipment and facilities, without mentioning the need for qualified personnel for the operation. Thus, the development of a reliable, simple, rapid and low cost method is required. This work was intended to prove the efficacy of the gravimetric method for the determination of fuel in lubricant oil. Such verification was conducted by comparing the results obtained through gravimetric and chromatographic methods. In this regard, both results were similar between each other being that the gravimetric method results were closer to the theoretical ones than those of the chromatographic method.