Crude oil with different concentrations was subjected to Pseudomonas species at 37 degrees C and various incubation periods. The results showed that Pseudomonas species grew faster at 1% (v/v) concentration of crude oil and exhibited high biodegradation ability within 1 week. On measuring the emulsification activity and emulsion stability during different stages of growth, in various immiscible hydrocarbons, it appeared that the species was able to produce a stable emulsion with a maximum at the end of stationary phase of growth. The gas chromatography analysis of the saturated hydrocarbons of crude oil showed that, an increase in concentration of iso-alkanes in the range of C15-C20, and a bioconversion of heavy iso-alkanes in the range of C21-C22+. Chemical analysis of crude oil by liquid chromatographic technique before and after growth showed that, the saturated alkanes were more degradable than aromatic and asphaltenic compounds. Treatment by Pseudomonas species may possibly be an effective method for the biodegradation of heavy paraffinic hydrocarbon leading to an enhancement in crude oil properties.