High uncertainty is a universal characteristic of modern economic reality. Therefore, the behavior of oil and gas companies requires special prudence in the disposal of assets, interaction with the environment of their localization, implementation of production and project activities. Accordingly, the basis for the choice of decisions and actions of the managerial level today should be an adequate scientific and methodological basis, based on the system properties of the oil and gas company and allowing to measure the stability of subsystems and their contribution to the overall ability of the industrial enterprise to work effectively in turbulent conditions and to withstand the enormous pressure of rare and hard-to-predict events. The purpose of this study is to develop and validate a methodology for assessing the sustainability of an oil and gas company, which (unlike traditional ones) is based on the systemic economic theory and considers sustainability as a result of the interaction of subsystems of object, environment, process and project types, their potentials and their combined contribution to the overall sustainability of the enterprise. The methodology is based on the systemic economic theory as a scientific basis for ensuring the viability of oil and gas companies in conditions of high uncertainty. The order of counting the generalized criteria of stability of subsystems of an oil and gas company is based on the consistent use of the method of hierarchy analysis by T. Saaty and multidimensional comparative analysis. The integral indicator – the index of oil and gas company sustainability – is calculated on the basis of the index method using geometric average by U. Jevons, interpreted with an interval method. Approbation of the methodology for assessing the sustainability of oil and gas companies was carried out on the basis of the data on oil and gas companies operating in foreign markets. The results of calculations showed different levels of stability of individual subsystems of oil and gas companies. In particular, the project-type subsystem, the fragility of which is caused by the resource-raw material model of business conduct, requires special attention from the management of Russian companies; foreign companies – the subsystem of the environmental type, the viability of which is determined by the potential of oil and gas assets. Recommendations for the formation of a model of behavior of an oil and gas company taking into account the level of its sustainability are suggested.