The use of biological fuels based on vegetable oils and other similar raw materials in diesel engines in developed countries can reduce the cost of mineral diesel fuel and improve the environment. This issue is relevant for Ukraine as well, in connection with which the governing bodies pay great attention to it. The deepening of knowledge in the study of the peculiarities of the flow of operating cycles of diesel engines, their power and toxic characteristics at the same time contributes to the optimization of the use of these types of fuel. In this work, the main issues related to the use of vegetable oils, such as sunflower, rapeseed, corn oils and their ethyl esters, both in pure form and in a mixture with mineral diesel fuel, are considered as a biological component of fuel. Theoretical issues and experimental data related to the use of these fuels in diesel engines are considered. Experimental studies were carried out on diesel engines D21A and four-cylinder - Skoda - an analogue of the 1.9-liter Volkswagen engine with turbocharging. Economic and toxic characteristics were obtained by load and speed characteristics. There is an increase in the consumption of mixed fuel in comparison with mineral fuel, the toxic characteristics were better in some indicators, in some cases, for example, when operating at increased capacities, they worsened relative to those when operating on mineral fuel. The basic principles of the effective use of biofuels in transport diesel engines are formulated in terms of energy and toxic indicators, as well as the corrosive effect of blended biofuels on fuel equipment. Today, gas stations in Ukraine only sell alternative fuels for gasoline engines. These are mixtures in various proportions of gasoline and bioethanol with a content of the latter up to 35–40% by volume. The price of such fuel is lower than the price of gasoline. Biodiesel fuels are not commercially available, although they would also cost less than mineral diesel fuel. It is likely that the use of biodiesel fuels is restrained due to the need to adapt the diesel engine to these fuels and to monitor the state of the fuel equipment. However, these costs are small and can be easily compensated for by the difference in the price of mineral and biodiesel fuels. It can be assumed that, first of all, biodiesel will be introduced into agricultural machinery.