A 95-day field trial on the bioremediation of oil in beach sediment using Osmocote and chitosan was conducted on an inter-tidal foreshore in Singapore. Osmocote was the key factor in enhancing nutrient levels in sediments, the metabolic activity of the indigenous microbial biomass, and the biodegradation of aliphatics and polycyclic aromatic hydrocarbons (PAHs) with ring number of 2 and 3. In contrast, chitosan did not enhance these parameters in the presence of Osmocote. However, the addition of chitosan to Osmocote amended sediments significantly enhanced biodegradation of recalcitrant 4-6-ring PAHs. This is most likely due to the high oil adsorbancy capacity of chitosan, which enhances the bioavailability of high ring number PAHs to the microbial biomass.