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Graphical abstract Abstract The objective of this study is to investigate the differences of emulsion stability evaluated by phase separation proportion and Turbiscan Stability Index (TSI). The relationship between emulsion stability and oil displacement efficiency was also investigated. An alkaline-surfactant-polymer (ASP) solution and a surfactant-polymer (SP) solution were both selected to prepare emulsions, respectively. The instability process of emulsions was studied by the multiple light scattering as well as the bottle test. The opposite stability results, evaluated by the TSI and the phase separation proportion separately, of same emulsion are observed. The discrepancies resulted from diverse influence of emulsion instability types in test methods. The main instability type in ASP emulsions is creaming, whereas in SP emulsions is flocculation and coalescence. The influence of creaming is more notable in bottle test. However, in TSI calculation, not only creaming but also flocculation and coalescence are recorded and counted particularly. The stability results obtained by the bottle test and the multiple light scattering method were similar for emulsions prepared with different concentrations of ASP or SP solution. Injection pressure change in core flooding experiments can be better explained by TSI of the emulsion. [ABSTRACT FROM AUTHOR]