Surfactant flooding is one of the most promising techniques to recover oil from unprofitable reservoirs. Surface-active ionic liquids can overcome the limitations of the current surfactants. The rheology of the injecting solutions and the formed slugs is critical in the evaluation of an enhanced oil recovery process. The thermo-rheological behavior of a biodegradable surface-active ionic liquid, [ProC(4)]DS, and the corresponding binary and ternary mixtures with water and n-octane was studied. All flow curves exhibited shear-thinning and thixotropic behavior. The viscoelastic behavior of the ternary samples depended strongly on the [ProC(4)]DS content. Three different regions were identified: typical liquid-like behavior, weak gel, and true gel. The thermal profiles indicated that the tested systems were fully thermoreversible.