This thesis outlines exhaust gas emissions of motor vehicles powered by gaseous fuels and their impact on the environment, especialy on passenger vehicles (M1 category) powered by liquefied petroleum gas (LPG). The paper gives a brief description of internal combustion engines powered by most commonly used gaseous fuels on the Croatian and global market. Since the data about emissions and proper functionining of exhaust gas after treatment systems for such vehicles is not registered nor processed in Croatia, as there is no legal basis for it, the goal of the research is to check their impact on the environment. In fact, in Croatia such vehicles are not required to pass the Eco test during regular technical inspection of the vehicle. In the thesis are descriptions of existing types of gaseous fuels that are used in Croatia, their compositions, compositions of their emissions produced by combustion, advantages and disadvantages of gaseous fuels and other important features related to motor vehicles powered by such fuels. The plan was to conduct two different vehicle tests, one by the Croatian Vehicle Centre (CVH), and the other by the Faculty of Mechanical Engineering and Naval Architecture in Zagreb (FSB) in their Laboratory for engines and vehicles. Unfortunately, due to a short period of available time, the test by FSB was not successfully conducted. The conducted tests by CVH are essentially measuring of exhaust gas emissions of vehicles powered by LPG, and processing of the resulting data. Particularly interesting are the data related to historical data. This refers to emissions evaluations depending on vehicle’s mileage, respectively vehicle’s age. It is expected that the results of the analysis will be able to determine what impact does the age of vehicles powered by LPG have on vehicle’s emissions. As a theoretical approach to this problem, an analysis has been made in a software package named Copert, whose analysis shows what impact these vehicles have on the total emissions of passenger vehicles in Croatia. Data about the vehicle structure in Croatia necessary for this analysis was obtained also from the CVH, which shows that their participation was of significant help for the making of this thesis.