Like other kinds of projects, construction projects are exposed to uncertainty, which plays a critical role in determining the transaction cost (TC). This study explores the uncertainty factors that are associated with construction projects that substantially influence the TC. To obtain the opinions of construction professionals, a survey questionnaire was developed after identifying 30 relevant causes of uncertainty from the literature. A survey of 216 professionals was conducted in Pakistan, and the relative importance index (RII) was used to prioritize the significant uncertainty factors that escalate the TC. Based on the responses from various construction professionals, this study determined that the most significant uncertainty factors that influence TC are: competitive tendering, incomplete design and specifications, late payments, conflict management, delayed possession of sites, force majeure, and work acceleration. This study also compared and analyzed the views of project managers and consultants and found that uncertainty from internal sources has a more significant influence on TC than that from external sources. The political and environmental groups do not contribute much escalating the TC. However, uncertainties that arise from the commercial, project site, and technical groups are more of an influence on TC. This research helps practitioners and professionals to adopt integrative systems in most uncertain situations proactively to find opportunities in volatile markets to reduce the impact of uncertainty on the total project cost.