Changes in the business conditions of gas industry enterprises and the regulatory framework for the creation and operation of energy facilities require the development of the energy infrastructure of production facilities. The diversity and a large number of existing energy facilities, as well as the use of a risk-oriented approach to the gas industry management lead to the need to create decision support systems for the strategic development of the energy infrastructure of production facilities on an industry-wide scale. The purpose of the study is to develop a set of mathematical models for calculating the index of the technical condition of energy complexes of production facilities used to prepare structured information as a part of a decision support system creation for the strategic development of the system, which will allow us making a decision on the minimum required volume and timing of reconstruction of the energy infrastructure of a production facility under modern conditions with restrictions on the reconstruction budget. The solution of such a multi-criteria problem required: justification of a set of admissible solution alternatives, risk assessment when making specific decisions, development of a system and mathematical dependencies for assessing the criterion indicators that make up the technical condition index taking into account preferences and decision rules, as well as the rules for calculating the weight of the assessment components in the value of the integral indicator. Based on the developed mathematical models, an algorithm for the technical condition index determination of a single energy complex of a production facility was formulated, which is an integral part of the generalized algorithm for applying the mathematical support of the decision-making system for the strategic development of the energy infrastructure of gas industry enterprises.