Abstract: A computer model for simulation of oil slick transport inseas by a Lagrangian discrete parcel algorithm is proposed. Oil spilled in awater body, regardless of whether it is originated as a surface or subsurfacespill, consists of a floating surface slick and suspended oildroplets in the water column. In this algorithm the oil slick is viewed as alarge number of small parcels of equal mass and their discrete path and massare followed and recorded as functions of time relative to a reference gridsystem in space. The movement of each parcel in the sea is affected by thewind, water current, and concentration of surrounding parcels. The transport of spilled oil is governed by advection, horizontal spreading,turbulent diffusion, evaporation, dissolution, emulsification, theinteraction of oil with the shoreline, and sedimentation. In addition,photochemical reactions and biodegradation can also affect thecharacters of the oil andreduce the amount of oil over a long period of time. The model simulatesboth continuous and instantaneous oil spills, not only oil spills, butalso ofother toxic matter. American Princeton Ocean Model is applied in thispaper as the hydraulic model. Sample simulations for oil spills in Bohai arepresented.