Among the urgent problems of oil and gas producing enterprises in Western Siberia is the low level of condition of vehicles, a significant part of which is operated in excess of permissible service lifetime standards. One of the main method to increase the efficiency, reliability and safety of vehicles is to limit the maximum lifetime of their operation. The purpose of the research presented in this article is to develop a methodology for determining the rational service life of vehicles, ensuring an increase in the reliability of functioning of transport and technological systems of oil and gas producing enterprises in Western Siberia. The scientific novelty consists in establishing patterns and creating mathematical models of the impact of age and operating time on the coefficient of technical readiness of automobiles. The methodological basis of the article is the systematization of research papers, regulatory documents, scientific and technical publications, as well as elements of a systematic approach, methods of expert assessments, mathematical statistics and economic analysis. It is revealed that all the considered methods for determining rational service lifetime have a limited scope of use. It is proposed to set the operating time limits using a method that, unlike most of the known ones, takes into account the impact on the technical readiness coefficient not only of operating time from the beginning of operation, but also of the intensity of vehicle use. It is illustrated that, in general, there is no statistically significant linear correlation between the age of vehicles and their operating time since the beginning of operation. One-factor and two-factor model patterns of the impact of these indicators on the coefficient of technical readiness have been developed. The validity of the proposed models has been verified, numerical values of their parameters have been established. The obtained correlations made it possible to develop a methodology for determining the maximum age limit of vehicles, taking into consideration the intensity of their use. The effect is formed due to a more accurate determination of the service lifetime of automobiles, which affects the increase in the coefficient of technical readiness. Further research in this area will be aimed at developing a methodology for adjusting the vehicle service lifetime with consideration to their operating conditions.