Total world demand for tuna has increased rapidly over the 1956-66 period. These increases in demand are due to rising populations and expanding per capita income in the principal tuna-consuming countries such as the United States, Japan and the E.E.C. countries. This paper attempts to discover the relationship between per capita tuna consumption, tuna prices and real per capita income for the nine leading tuna-consuming countries. On the basis of these relationships the world demand for tuna is projected to the year 1990. When projected increases in population and standard of living (i.e., per capita income) are accounted for over the next twenty years, it is estimated that tuna consumption will rise from 1,320,000metric tons in 1966 to approximately 5,000,000 metric tons in 1990 assuming the existence of 1966 prices throughout the projection period and available world supplies. If the maximum sustainable yield of tuna on a world basis is no more than 2,600,000 metric tons and additional increase in world production is likely from only the skipjack resource, it is very likely that cost and prices will rise and demand will be reduced. Assuming a world price elasticity of unity for tuna, it is estimated that by 1990, world demand and supply will be equal at an ex vessel price of over 38 cents per, pound and consumption of about 2,100,000 metric tons under existing technology of harvesting the tuna.resource. In this event, technological change through gear and biological research may bring about an expansion of the world tuna fishery and reduced prices. However, this research and development must be accompanied by a vigorous fishei7 management program to prevent the destruction of.the resource. Without thib fishery management program,.technological change can only bring long run negative returns to the world tunaconsuming and producing nations.