This dissertation examines greenhouse gases from ships calling at U.S. ports. It calculates the marginal cost of reducing vessel emissions and evaluates policies targeting reductions. Ship profit models show speed reduction costs are higher than carbon prices. A 20% emissions cut with $250/ton fuel generates $15-275/ton in marginal costs. Larger overseas projects offer greater cost advantages for offsets. Models quantify relationships between ship speed, size, power and transportation costs. Requiring all ships to cut emissions may cost developing countries $6.1-6.7 billion, while differentiated responsibilities raise equity issues. Subsidizing developing countries may better reduce emissions efficiently.