Trinidad and Tobago is undergoing substantial economic growth resulting from petroleum revenues, the volume of transportation (including air travel) thus expanding rapidly. It is essential, therefore, to provide estimates of future traffic to allow sensible planning to be undertaken. Previous modelling work in this region has tended to be extrapolative. This paper describes work undertaken to evaluate the underlying causal relationships influencing the volume of air travel to the small (population 1.1 millions) twin-island Caribbean republic and to build a descriptive model. The well-tried method of multiple regression analysis was used. Locally available statistical data were utilized, the analysis revealing that airfare, per capita income, and population were the main influencing factors. Cultural ties between zones were taken into account, postwar migration emerging as a proxy variable to accommodate this. Backward projections were made using the calibrated equation and intuitively reasonable forward projections were derived. The paper contains as examples detailed descriptions of the results relating to four of the links studied as well as a presentation of overall results. The technique appears appropriate both to a rapidly changing economic environment and to small nations (for example, other Caribbean islands) in deriving projections for the design of air transport facilities and the planning of services.