A direct insertion scheme for assimilating coastal acoustic tomographic (CAT) vertical temperature sections into a multilevel, coastal primitive equation model for the Gulf of Sirte (Lybia) is investigated using computer simulation experiments. Although the model was developed for the whole Mediterranean Sea (MED), only a model sub-domain covering the Gulf of Sirte was used in this study. The model has realistic coastlines and bottom topography, and a coastal-following, curvilinear, nearly orthogonal, horizontal coordinate system with a horizontal resolution of about 10 by 10 km. The grid of the model was designed using a grid generation/focusing technique. The model has complete thermodynamics, second order turbulence closure, and 16 bottom-following (sigma) vertical levels. To generate the true ocean for this study, the model was first spun up for 30 days with the Levitus temperature and salinity and ECMWF wind climatologies, and then run for one year and more. The last 60 days of this control run were taken to represent actuality.