Investigations on the effect of oils on the oxidative stress and antioxidant molecules in gills of Perna viridis were carried out under controlled laboratory conditions. For this purpose water accommodate fraction of diesel oil at 0.5 arid 5% were tested for cell damage and antioxidant responses in P. viridis for over 15 day period. The parameters measured included lipid peroxidation (LPX), superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPX), glutathione reductase (GR) and glutathione-S-transferasa (GST), as indices of oxidative stress. Induction of oxidative stress in tissues was evidently seen by increased LPX. Antioxidants responded positively in a tissue specific manner indicating their involvement in counteracting oxidative damage. Thus these antioxidant responses would serve as the relevant biomarkers for detection of oil pollution and hence recommended for use in environmental monitoring programmes.