In an effort to advance the understanding of value of reliability (VOR) in freight transportation, this paper provides a comprehensive review of existing studies. This study focused on reliability measures adopted by various studies, the theoretical and mathematical foundation of modeling the valuation of reliability, and the contributing factors that influence the values. Since nearly all the studies in VOR analysis employed stated preference (SP) surveys and the survey design directly affects the study elements and modeling approaches, this synthesis pays close attention to the various survey design components. Through a comparative analysis among existing studies, this paper aims to shed some lights on the potential factors that contribute to the variations in VOR estimation. The results indicated that the estimated VOR values varied largely from one study to another; probably due to the use of different units, reliability measures and survey design approaches. This review showed the complexity and challenges faced when studying freight users’ VOR. Insufficient data has also been cited as a major obstacle to advances in the understanding of how the freight industry values travel time reliability. Furthermore, the large variations in the VOR values indicate the need for further research efforts in this area.