The maritime oil tanker routing and scheduling problem is known to the literature since before 1950. In the presented problem, oil tankers transport crude oil from supply points to demand locations around the globe. The objective is to find ship routes, load sizes, as well as port arrival and departure times, in a way that minimizes transportation costs. We introduce a path flow model where paths are ship routes. Continuous variables distribute the cargo between the different routes. Multiple products are transported by a heterogeneous fleet of tankers. Pickup and delivery requirements are not paired to cargos beforehand and arbitrary split of amounts is allowed. Small realistic test instances can be solved with route pregeneration for this model. The results indicate possible simplifications and stimulate further research.

The split pickup split delivery crude oil tanker routing and scheduling problem is a difficult combinatorial optimization problem, both theoretically and practically. However, because of the large expenses in crude oil shipping it is attractive to make use of optimization that exploits as many degrees of freedom as possible to save transportation cost. We propose a nested column generation algorithm for this particular split pickup split delivery problem which bears several complexities such as a heterogeneous fleet, multiple commodities, many‐to‐many relations for pickup and delivery of each commodity, sequence dependent vehicle capacities, and cargo quantity dependent pickup and delivery times. Our approach builds on a branch‐and‐price algorithm in which the column generation subproblems are solved by branch‐and‐price themselves. We describe our implementation in the branch‐cut‐and‐price framework SCIP and give computational results for realistic test instances. The high quality schedules we obtain for these instances improve on those in previous studies. © 2012 Wiley Periodicals, Inc. Naval Research Logistics, 2012

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