Security-related risks of oil and gas pipelines are assessed in this paper using the technique of game theory in combination with a security risk assessment approach. A Socio-political index is defined and embedded in an innovative and comprehensive assessment method, considering the effects of social, economic and political elements on pipeline attractiveness and vulnerability. After having analysed the security threats, security measures, aimed at increasing the security level of a pipeline system, are assessed by using a game-theory model. The pipeline segments which are the most probable to be attacked are determined. In addition, having assessed the possible outcomes of attacks to each segment, the security of different segments of specific pipeline routes can be further improved. Our approach can efficiently allocate limited security resources to decrease the security risk along a pipeline route. It should be noted that although this study focuses on oil and gas pipelines, the proposed methodology could be easily adapted to other pipeline systems.