The enhanced oil recovery (EOR) potential of different alkylbenzenesulfonate surfactants was investigated in a combined study of crude oil-water phase behavior and interfacial tension (IFT) and macroscopic oil displacement studies. In the presence of small amounts of calcium ions (calcium/sodium = 4 mol %), ultralow oil-brine IFT (<0.001 mN/m) was observed at ionic strengths 10 times lower than "optimal salinity" with sodium chloride only; this suggested an application in low salinity surfactant (LSS) EOR. "Optimal ionic strength" was determined for different calcium/sodium ratios in the brine, which further allowed prediction of phase behavior and IFT range for a given surfactant and a given crude oil at different brine compositions. In laboratory core floods, crude oil displacement by LSS with an optimal ionic strength electrolyte was around 9% higher than at "non-optimal" conditions.