In this study, the effect of sodium hydroxide (NaOH) and sodium silicate (NaSiO4) solutions for the improved oil recovery of Garzan (26 API degrees) and Raman (17.2 API degrees) crude oils with variable salinity of the alkaline solutions, and the effect of injection flow rate at the salinity values of the alkaline solutions that yielded maximum oil recovery for both crude oils has been investigated using a one-dimensional unconsolidated limestone reservoir model. As the previous study, the interfacial tension measurements of the given crude oils and alkaline solutions interface have been measured to find the optimum concentrations of the alkaline that give the minimum interfacial tension at the crude oil/alkaline solution interface, at different salinity of the alkaline solutions. Using these optimum alkaline concentrations, 22 displacement runs have been performed; 13 runs with the variable salinity of the alkaline solutions, six runs with the variable injection flow rate, and the remaining three runs were the base floods, performed without oil to see the interaction of alkaline solutions with the porous matrix. The results of the displacement tests showed that the NaOH solutions with increasing salinity, has given the most significant incremental oil recovery, about 3-9% for Garzan crude oil, while the NaOH and NaSiO4 solutions with different salinity did not produced any significant incremental oil recovery for Raman crude oil, when compared with the base waterfloods performed for each crude oil types. Six displacement runs have been performed; three runs for Garzan crude oil and three runs for Raman crude oil at injection flow rates of 400, 300, 200 and 100 cm(3)/h for each crude oil with the salinity of the alkaline solution that yielded maximum oil recovery. The results of the displacement tests showed that injection flow rate of alkaline solution has an important effect on Garzan crude oil and has less effect on Raman crude oil in the scope of oil recovery achieved. The optimum injection flow rates for both Garzan and Raman crude oils have been found, which was 200 cm3/h for Garzan crude oil and 300 cm3/h for Raman crude oil for our model. (C) 2000 Elsevier Science B.V. All rights reserved.