CO2 fixation by microalgal cultures, a potential method for CO2 emissions mitigation, was studied in small (approx 2 m(2)) ponds using actual flue gas from power plant whose fuel is low sulfur heavy oil. Three algal stains were cultivated under semicontinuous dilution (30-50% dilution every 2-3 d) in seawater over a period of almost one year, in both a temperature controlled greenhouse and outdoors under ambient temperature conditions. Two algal strains (Nannochloropsis salina and Phaeodactylum tricornutum), obtained from a culture collection, required frequent (every 10-30 d in summer) cultures restart due to suddenly decrease of algal productivity. One strain (Tetraselmis sp.), isolated from local seawater, could be cultivated for over 150 d under fall and winter conditions. Laboratory experiments were carried out to measure algal productivity as a function of Standing biomass. The data was fitted to a derived equation that relates algal productivity to incident light intensity and Standing biomass. There was a reasonable correlation between the calculated and measured outdoor pond productivity.