The paper presents investigations on damageability of agricultural tractor power unit fed with rapeseed oil, with the use of Event Tree Analysis – ETA. The work aimed at: evaluation of occurrence probability for the unfavorable events in the case of feeding engine with unprocessed rapeseed oil, checking the effects of applied protective systems and propositions of more effective protective solutions. The following initializing events were distinguished in the system: water content in rapeseed oil, mechanical and bacteriologic contamination of rapeseed oil. The event tree was developed for each initializing event. The quantitative analysis of damageability was carried out by calculating of result probability in each branch of event tree. There were used the safety barriers to reduce the negative results of occurrence of the initializing events in the forms of: appropriate procedures, tractor operator activities, and devices mounted in the fuel system. An example of such anticipated safety measure is the proposition of installation of special water separator in the fuel system as well as recommendations for tractor operator, who should undertake the specific actions under the determined situations.