In this paper, the three different approaches to the modelling of large scale 3-dimensional flow in the ocean such as the diagnostic, semi-diagnostic (adaptation) and the prognostic are discussed in detail. Three-dimensional solutions are obtained for the circulation during winter of the western part of Indian Ocean north of 20 degrees S and west of 80 degrees E using diagnostic and semi-diagnostic models. Both the models computed realistically well the persistent major currents during winter in the upper levels of the ocean. The semi-diagnostic calculations showed that the velocity fields were smoothed and unrealistic currents were removed in the model domain, especially in the Somali and equatorial regions during the adaptation stage. Temperature and salinity anomaly fields showed that the climatic temperature and salinity data used to drive the model has also been smoothed considerably during the adaptation stage.