Jatropha biodiesohol (JBH) is an alternative microemulsion-based fuel that promotes the use of non-edible vegetable oils and bioethanol, replacing fossil fuel consumption. Unprocessed vegetable oil is more eco-friendly than transesterified biodiesel, which consumes a substantial amount of chemicals, energy, and water. However, this unprocessed vegetable oil has a limitation on the injection system of diesel engines because of its high viscosity. Microemulsification technique is introduced to alleviate this problem by adding an alcohol ethoxylate surfactant (LS) and bioethanol. The ethylene oxide group (at LS1, LS3 and LS7) of the surfactant, the ratio of the ethanol-surfactant (E/S ratio), and the ethanol and surfactant content (E/S content) were studied to improve the miscibility of Jatropha biodiesohol. To screen for the optimum product, those factors forming a water in oil microemulsion with transparent, clear, and homogeneous JBH were screened for in phase behavior experiments and kinematic viscosity experiments. LS1 is the most appropriate for solubilizing all components because of its low HLB (hydrophilic-lipophilic balance). The increase E/S ratio and E/S content enhance the reduction of the kinematic viscosity. A mixture design was applied to optimize the composition of each component to predict the desired kinematic viscosity. Compared with the other models, the results indicate that the full cubic model of a {3,3} simplex lattice model with three interior points and a centroid in the mixture design (providing) displayed the best fit when screening and optimizing the kinematic viscosity with R-2 = 0.998 and MAPE = 5.031%. (C) 2015 Elsevier Ltd. All rights reserved.