Simultaneous extraction and transesterification of oil from rape seeds using a mineral diesel and butanol mixture have been performed to obtain a mineral diesel and biodiesel mixture that is currently used as fuel. Lipozyme RM IM is an enzyme preparation well known for having major catalytic activity during oil transesterification. The response surface method was used to optimize the process of simultaneous oil extraction and transesterification. We aimed to not only extract the maximum amount of oil from rape seeds, but also to transesterify the whole amount using butanol. We determined that the optimum conditions for simultaneous oil extraction and transesterification using butanol were as follows: molar butanol to oil ratio-31:1, amount of ferment preparation Lipozyme RM IM-52%, duration-19.6 h, temperature-40 degrees C, and mineral diesel to oil ratio (w/w)-9:1. (C) 2015 Elsevier B.V. All rights reserved.