In this work, alcohol-free surfactant formulations incorporating sodium alkyl alkoxy sulfate surfactants and a sodium alkyl ethoxy sulfate surfactant are tested at 52°C for reservoir brine having a total dissolved solids of above 300,000mg/L with total hardness of about 13,000mg/L. The optimized surfactant formulations show excellent aqueous phase stability, produce an ultra-low-interfacial tension (IFT) of 0.004mN/m, and give fast coalescence rates of less than 30min at reservoir salinity and temperature. Surfactant-only sand pack studies further validate the formulations by mobilizing about 60% of residual oil without mobility control. In addition, the hydrophilic lipophilic deviation (HLD) method is used to find the optimal surfactant/co-surfactant ratio (defined as the ratio giving the lowest IFT) at the reservoir salinity and temperature. Results show, first, that HLD constants measure at low salinity are applicable at high salinity and high hardness, and second, that the correct determination of surfactant head constant ‘K’ and temperature constant ‘αT’ governs the precision of the HLD approach as a surfactant selection tool for chemical enhanced oil recovery (cEOR) application. Results illustrate the potential of surfactant-only flooding to produce significant tertiary oil recovery.