Utilizando datos de la Expedición EASTROPAC, se estudiaron las principales masas de agua presentes en el Océano Pacífico Tropical frente a Costa Rica. Fueron encontradas el agua superficial tropical (AST), el agua subsuperficial subtropical (ASS), caracterizada por un núcleo de alta salinidad con valores superiores a 34,9% y el agua intermediaria antártica (AIA), que se caracteriza por presentar un mínimo relativo de salinidad del orden de 34,55%.  The main water masses in the Tropical Pacific Ocean in front of Costa Rica have been studied.  The subsurface water masses were analized using the Core Layer Method. The matter masses found in this area were: 1. The Tropical Surface Water, 2. The subtropical Subsurface Water, characterized by a high salinity core valve graeter than 34,9%  and 3. The Antarctic Intermediate Water, characterized by a salinity minimum close to 34, 55%