Of all current proposals for sustainable transportation, the assumption is energy scarcity when there are economically favorable alternatives using existing technology. This paper explores the economics of a sustainable transportation energy pathway that provides carbon-neutral and carbon-negative synthetic fuel derived from seawater as the feedstock and power via Ocean Thermal Energy Cycle (OTEC). Seawater-based synthetic fuel is naturally carbon-neutral - different synthesis processes can yield hydrogen, methane, methanol and ethanol as well as gasoline, diesel or jet fuel - and is carbon-negative when combined with aquaculture. Methanol is favored as a fuel as it requires relatively lower capital investment; can be easily transported and stored; can be used as a feedstock to many chemical processes that currently rely on petrochemicals; and can be coproduced with or converted to dimethyl ether. This paper proposes a new process that for the first time marries OTEC-power and seawater-based-methanol synthetic fuel generation. The proposed process is optimized for highest product yield for a given capital investment, in that operating costs and therefore product costs are dominated by capital cost amortization. The methanol fuel produced by this process within the amortization period has a cost per unit of energy potentially comparable to petroleum-derived gasoline or diesel fuel and post-amortization to natural gas. The economics of this new process is compared to prior synthetic methanol processes proposed by Meyer Steinberg and William Avery.