Oil refining is one of the most complex chemical industries; the objective of refinery operations is to generate as much profit as possible by converting crude oils into valuable products. The current trend toward processing petroleum needs sufficient compositional information to understand the chemistry of reactions that are involved. The objective of the present paper is to review the simulation technologies and characterization techniques which have been used in refining industry. It is found that simulation can be used in crude oil scheduling, predicting wax precipitation, asphaltene deposition, and for fractionation of crude oil based on equilibrium stage relations. The review on characterization methods clearly illustrates that the spectroscopic techniques (IR/FTIR, NMR, NIR); chromatographic techniques; true boiling point; solvent precipitation; refractive index; differential scanning calorimeter and thermogravimetry; and near-infrared region are mostly used in characterizing crude oil.