The Network of Stand-By Oil Spill Response Vessels has been built up and maintained through regular procurements, which are open to all interested parties. In practice, most contractors are private companies linked to the shipping and oil spill response sectors. Although contracted by EMSA for response activities, the vessels are owned, crewed and operated by the contractors. During the contract period, the vessels should be available, upon request, to halt any commercial operations in which they are engaged, and undertake oil spill response operations.