Most of the debate associated to port-call coordination and optimization is related to container transport. As the nature of non-container port-calls differs, the characteristics of non-container segments need to be understood. The tanker industry largely offers a tramp service (like a taxi) with fixed, semi-fixed or unfixed routes without a pre-fixed timetable like in a liner service (like a bus).
This means unknown or unpredictable port visits until a freight contract is made by traders who decide load date and destinations depending on factors like oil prices. Due to fluctuations in prices and availability, there are often last-day changes of schedule which put pressure for port-call actors and resources to respond on time and create financial & environmental benefits to all involved.