In this paper, four nonionic binary mixed surfactant systems (Tween 80/Span 80, Tween 80/Span 85, OP 10/Span 80 and OP 10/Span 85) were used to emulsify water/octane mixture. The influence of emulsion composition and preparation method on the stability of water-in-octane emulsion was investigated systematically. The mixture of Tween 80/ Span 80 had the best synergistic effect. Those mixed surfactant systems with HLB = 9 stabilized water-in-octane emulsion the best. Under optimal condition, water-in-octane nano-emulsion (the effective diameter of water droplets = 200 nm) could be made. These water-in-octane nano-emulsions could be stored for more than 26 days at 25 degrees C without phase separation. (C) 2010 Elsevier Ltd. All rights reserved.