In this article, there is resumed the accomplished impact analysis of biodegradable tractor oil HYDROS UNI application in gear - hydraulic circuit of the tractor Zetor Proxima 7441. This analysis was performed by comparative testing with standard mineral oil PP 80 on the basis of decelometric trials. Decelometric trials were carried out with measuring device XL - MeterTM Pro Gamma. The measurements were executed by the 3rd and the 4th unreduced gear. The results show that the oil HYDROS UNI does not affect decelometric characteristics of the tractor Zetor Proxima 7441