Harmful exhaust fumes from cars are one of the main topics of the future due to the consequences they leave on the environment. Therefore, this paper presents and explains various measures that can reduce the amount of exhaust gases in four-stroke engines. This paper covers measures for diesel and otto engines. The principle of work of engines with different processes is also presented, as well as the explanation of the temperatures and pressures inside chambers of combustion gases during the four strokes. Euro standards are the requirements of the European Union with which they try to introduce new measures every year so that each newly produced car has less exhaust gases than the previous car. There are very similar measures inside and outside the engine in both otto and diesel engines that help reduce exhaust fumes. This paper has a lists of the measures and which exhaust gases they reduce. The paper has a lists of both harmful and non-harmful exhaust gases that occur during engine operation and their consequences for human, plant and animal life. Alternative fuels are also shown with some alternative fuels that are currently used and which could be used in the future. This paper shows also possible problems with individual alternative fuels. Vehicles that are a product of the automotive industry in Croatia, but also in the world, are also listed. In all countries of the European Union, there is an stimulus to buy electric vehicles because such vehicles are considered the vehicles of the future.