World annual petroleum consumption and vegetable oil production is about 4.018 and 0.107 billion tons, respectively. Vegetable oils from bio-renewable oil seeds can be used when mixed with diesel fuels. Vegetable oils can be used as fuels for diesel engines, but their viscosities are much higher than usual diesel fuel and require modifications of the engines. Different ways have been considered to reduce the viscosity of vegetable oils, such as dilution, microemulsification, pyrolysis, catalytic cracking, and transesterification. Compared with transesterification, pyrolysis process has more advantages. The liquid fuel produced from pyrolysis has similar chemical components to conventional petroleum diesel fuel. Vegetable oils can be converted to a maximum of liquid and gaseous hydrocarbons by pyrolysis, decarboxylation, deoxygenation, and catalytic cracking processes.