We consider the strategic level routing problem of hazardous materials in marine waters over a multicommodity network with multiple originsdestinations. The problem is motivated by the fact that selecting optimal routes by each origindestination pair or by each type of material is myopic and may result in overloading certain links of the transportation network and, consequently, in poor overall system performance. We employ a network flow model, instead of the traditional shortest path formulation, to capture the multicommodity, multiple origindestination nature of the problem. An efficient two-phase solution approach is proposed. The proposed solution methodology is illustrated through a single hazmat problem followed by a large scale case study of the marine transportation system of oil products in the Gulf of Mexico.