The general characteristics of the seasonal variation of the thermohaline properties of the continental shelf water off Rio Grande do Sul, under non-conservative and quasi-synoptic conditions were analysed. The method applied - volumetric statistical T-S analysis allows the computation of the water masses budget from the knowledge of their temperature and salinity ranges. The data of 194 hydrographic stations from six oceanographic cruises between April 1968 and March 1969, were used. Water of Tropical and Subtropical origin (47,5% and 64% of the total volume during the winter and summer, respectively) was always present during the observation period. Subantarctic water has its maximum and minimum influences during the winter (15%) and summer (<3%), respectively. The average minimum and maximum temperature and salinity values of the water masses in the investigated region were observed in June (16,85ºC and 34,72‰), December (35,58‰) and March (20,82ºC).