The nature of working relationship between owner and contractor in engineering and construction projects is considered to have a major effect on the project performance. This research focuses on factors that may influence owner-contractor relationship effectiveness. Literature suggests that different types of contract, being one of these factors, tend to influence owner-contractor relationships. The aim of this research was is to clarify the role of different contract types on owner-contractor relationship effectiveness in industrial construction projects. A Q-methodology based study was performed to reveal the subjective perceptions of the project managers on the relative influence of various contract aspects and of other influencing factors of owner-contractor relationships. The influence of contract types on the relationships for project-specific situations was investigated by a project evaluation study. In this study, the relationship quality of four different projects was evaluated, using a relationship maturity assessment matrix. The research results show that contract type is not the tool to influence relationship effectiveness. The only contract aspects, which are identified as instrumental to improve the relationship, are contact aspects related to project structure specifying roles and responsibilities, and contract aspects about targeted criteria for performance.