Project Final Report-11123-24-Reservoirs containing very high total dissolved solids and high hardness make the design of a surfactant polymer (SP) flood difficult because surfactant tends to precipitate and separate under these conditions. In the proposed approach different surfactant formulations are evaluated. These formulations incorporate cosurfactants and co-solvents which minimize viscous macroemulsions, promote rapid coalescence under Winsor Type III conditions, and stabilize the chemical solution by reducing precipitation and phase separation. The optimal surfactant formulations are further evaluated in one-dimensional sand packs and coreflood tests using Berea sandstone, reservoir oils, and brines at reservoir temperatures. Lab studies will be performed to check phase behavior and fingerprinting from different areas within a reservoir to explore the reservoir characterization. Six multiple single well tests will be completed in two year periods to verify the robustness of new high TDS surfactant system and their effectiveness for mobilization of oil. Recommendations for improving the chemical flood design and minimizing the risk will be made.