In many sea ports, queue priority is determined by the first come first serve principle when the port is congested. The paper suggests that this principle should be avoided for environmental reasons, and suggests a simple alternative based on departure dates rather than arrival dates. This system will allow commercial beneficial trading of turns (slots) in the queue.In order to get the full benefit of the system, voyage charterparties to be adjusted, so that the demurrage does not work as a disincentive to environmental optimization. The paper includes suggested clauses.