Why do container ports and related maritime logistics organisations collaborate? Despite increasing research into supply chain collaboration (SCC), few valid and reliable instruments are available to measure accurately and objectively the multiple dimensions of SCC in maritime logistics contexts. This research aims to introduce SCC into maritime logistics as an intermediary supply chain process. It adopts comprehensive, rigorous and systematic procedures including item review, Q-sorting, pilot testing and confirmatory factor analysis (CFA) to develop and validate SCC measures. Practical instruments comprised 23 measures derived from a large-scale survey of 178 South Korean maritime logistics professionals. Empirical results indicate that a proposed model of SCC is statistically consistent, reliable and valid. Information sharing, knowledge creation, goal similarity, decision harmonisation and joint supply chain performance measurement were identified as factors that underpin SCC between ports and port users such as shipping lines, inland transport companies, freight forwarders, ship management companies and third-party logistics companies. This work extends the concept of SCC into maritime logistics, and offers managers insights into a self-diagnostic tool to shape effective collaborative relationships.