Knowledge about miscibility of injected gas in reservoir oils has a vital importance in gas injection process in petroleum reservoirs for enhanced oil recovery (EOR) goals. In other words, miscibility of the injected gas is highly depends on injection pressure and restriction of injection facilities. Thanks to these facts, minimum value of miscibility pressure should be specified accurately. To pass successfully the aforementioned issue, fuzzy logic method was utilized to specify minimum miscible pressure (MMP) of injected gas and reservoir oil. Moreover, different type of membership functions have been implemented such as curve shaped, triangular and trapezoidal shape. A large data banks which reported in open literature have been used in order to specify performance, deviations and precision of the developed fuzzy logic approaches. Furthermore, slim tube experiments have done on four different crude oil samples to determine their MMP values in contact with gas. Also, experimental results of this research have been matched accurately with corresponding outcomes of fuzzy logic approaches in comparison with conventional methods. According to the results gained from this research on the basis of statistical parameters, curve-shape membership function has higher superiority than other executed types of membership function. Outcomes of present work could be utilized for designing more precise, accurate and assured gas injection process by means of miscible displacement. (C) 2014 Elsevier B.V. All rights reserved.