The separation of a binary fluid mixture into its constituent phases involves the interaction of numerous physical phenomena. Studying such a transition gives insight into the underlying mechanisms, their respective strengths and at what stage in the separation each becomes important or dominant. Large scale simulations of three dimensional spinodal decomposition in a binary fluid using Dissipative Particle Dynamics show the approach to a linear time dependence in domain coarsening. We present interface and velocity maps which clearly demonstrate the Siggia mechanism for domain growth.