This paper presents the test results of a research on the use of a detergent additive in gasoline. The main objective was to find out the additive effect on carburettor cleanliness and gasoline consumption. To show this additive effect, three pairs of vehicles of different makes and types were subjected to controlled test on the roads in a fixed route and on the chassis dynamometer at two different constant speeds.Additional tests on a monocylinder engine, each time kept in the same operational conditions for comparison tests, were conducted to show the additive effect in a thermodynamic sense (if there are any).The test distance travelled by each vehicle during the whole test was approx. 10,300 KM The average time needed was approx. 314 hrs. with an average speed of approx. 33 KM/hr. The average fuel consumption for each vehicle was approximately 1,170 litre, while the average fuel saving was approximately 7%.The monocylinder test results were impartial.