Analytical Laboratory, Pharmacy Department, Faculty of Technology & Engineering, M. S. University of Baroda, Kalabhavan, Baroda-390 001 Manuscript received 8 December 1989, revised 28 June 1994, accepted 21 September 1994 The infrared spectroscopy has been used for characterisation of EOM, asphaltenes and crude oils of the Cambay basin. The functional groups of EOM, asphaltene and crude oil were characterised and extinction ratios at maximum wave numbers of the respective groups were calculated. On the basis of these data, the type of EOM, its evolution path and original organic matter of Cambay basin have been identified.