The production of oil and gas on the Norwegian continental shelf takes place at offshore installations owned and controlled by different operators, located in remote areas. Specialized platform supply vessels (PSVs) are used for servicing the installations with commodities needed for stable and continuous production. In current practice, each operator controls its own fleet of PSVs, and each installation is serviced from a dedicated supply base (among several) along the Norwegian coast where cargo demands are specified for each installation on particular days. In this work, we explore how costs and greenhouse gas emissions from the offshore logistics can be reduced by collaboration among operators through a sharing of their vessels and supply bases. We solve this by generating a priori a large set of feasible voyages that can be combined to form weekly routes for each vessel. Spot vessels can also be used to meet demands by performing the same voyages at a higher operational cost. A small numerical example based on real data is provided, illustrating a fuel saving that reduces emissions by more than 25% together with the possibility of also reducing the fleet size required to meet cargo demands.