ABSTRACT In this study the effect of brine salinity on the cloud point was investigated for a series of nonionic surfactants C13EOx (x = 7, 8, 9 and 10) at constant surfactant concentration (0.3 wt %) in presence and absence of an anionic surfactant (C12 C13PO3S04 Na) at different nonionic/anionic weight ratio (3:1, 1:1 and 1:3). In the absence of anionic surfactant, the results showed that the cloud point of the nonionic surfactants decreases as the salinity of brine increases. The relatively high ratio of the structure-making ions (Na+, Cl, HCO3 and S04) concentrations to the structure breaking divalent cations (Ca2+ and Mg2+) concentration in brines used may therefore be attributed to the overall decrease in the cloud point observed. After the addition of surfactant the cloud point versus salinity curves decrease with salinity and intersect at a critical salinity, Sc which found to be inversely proportional to the degree of ethoxylation of nonionic surfactants. Below Scr, the cloud point increases with anionic weight fraction. However, above Scr, an opposite behavior observed where the cloud point slightly decreases with increasing anionic weight fraction. Furthermore, the variation of the IFT with time in 0.3 wt% C13E010/C12-13(PO)SO4Na Wf = 3:1 and 1:1) mixtures at different salinity were tested. The results showed that at constant weight fraction as the salinity increases the IFT decreases. A linear relationship was obtained between the IFT and AT = TCP - TR, that the closer the surfactant cloud point to 51°C (temperature at which the IFT is measured) the lower is the interfacial tension at the oil water interface. Then, the potential of 0.3 wt% C13E010/C12-13(PO)&SO4Na (Wp = 3:1) mixture at 2.5 wt% salinity to alter the wettability and to increase the oil recovery in Benthimer sandstone cores was investigated using Amott-Harvey test and core flooding experiment. The results showed that the Amott-Harvey index reduced from 1.0 for brine to 0.86 in presence of surfactant showing the ability of surfactant to slightly shift the wettability of the system towards intermediate wettability. The core flooding experiment showed that the additional oil recovery form surfactant injection was 5.6% of original oil in place (OOIP) and the total oil recovery was 34.8% of original oil in place (OOIP).