In this study, the marine diesel oil-degrading bacterium strain NH1 was isolated and identified with respect to its 16S rDNA sequence as Pseudomonas aeruginosa with accession number KM267644. The ability of NH1 immobilized by entrapment in Ca-alginate gel to degrade different components of diesel oil contaminating seawater was examined in a batch system. The biodegradation rate of different components of diesel oil in free and immobilized cell systems can be ranked in the following decreasing order: total resolvable peaks (normal-and iso-alkanes) > the 16 polyaromatic hydrocarbons listed by the United States Environmental Protection Agency as priority pollutants > polyaromatic sulfur heterocyclic compounds > unresolved complex mixture (naphthenes, cyclo-alkanes, and aromatics). Kinetic modeling was performed to estimate the rate of biodegradation of each hydrocarbon type component. The biodegradation of diesel oil, total resolvable peaks and unresolved complex mixture was found to be best fitted with the second-order, while that of polyaromatic sulfur heterocyclic compounds and polyaromatic hydrocarbons followed the first-order kinetic model equations. The biodegradation rate of different components of diesel oil: aliphatics, polyaromatic sulfur heterocyclic compounds, and biomarkers (pristane, phytane, and 4,6-dimethyldibenzothiophene) was enhanced by immobilization, indicating the improved tolerance of the immobilized cells towards different toxic components of diesel oil. Storage stability and reusability tests revealed that the diesel oil degradation ability of the immobilized cells was stable after storage at 4 degrees C for 30 d and can be effectively reused for two batches of 56 d.