Esterification/transesterification two steps process is considered as the most widely used technology for biodiesel synthesis from waste cooking oil (WCO). However, this technology is currently explored in a single step process using supercritical technology due to its higher biodiesel yield and shorter reaction time. This paper presents experimental and simulation study of biodiesel production from high acid value WCO using supercritical methanolysis. The influences of four reaction parameters on biodiesel production including methanol to oil (M:O) molar ratio, temperature, pressure and time have been investigated. Response surface methodology (RSM) has been used to develop an empirical regression equation representing reaction variables function in response variable. Analysis of variance (ANOVA) has been used to examine the accuracy of the predicted model. Optimisation of reaction variables has been performed to maximise biodiesel production. The optimal conditions for 99.1% and 97.2% overall conversions of triglycerides and free fatty acids (FFA), respectively have been reported at 27.2:1 M:O molar ratio, 257oC temperature, 110 bar pressure and 17 min reaction time . A commercial simulation software (Aspen HYSYS) has been used to design and simulate the production process. The reaction has been simulated using the developed kinetic data at the concluded optimal conditions. A comparative analysis has been performed for results obtained experimentally, numerically and from simulation.