Continuous-velocity lattice gas cellular automata method is applied to the simulation of the motion of immiscible binary fluid. A new parameter is introduced which takes the magnitude of the segregation intensity of the fluid into account. Spinodal decomposition and droplet motion in a buoyancy field is simulated by the model. The simulations well reproduce the slow segregation of the phases and the deformation of the droplet. (C) 2004 Elsevier Ltd. All rights reserved.