Abstract: The transport of different petroleum products through a single pipeline is known as batch transfer, which is the most common method in product transportation. A certain amount of mixing between products is called interface contamination. In order to ensure the quality of the products being transported, the mixing volume and the position of the mixing zone should be accurately predicted. This paper estimates the mixing volumes by using a two-dimensional model of convection-diffusion equation, which  is solved by a two step method to obtain numerical solutions in laminar flow and turbulent flow, as  a comparatively effective method. The results show that the mixing volume in turbulent flow is smaller than that in laminar flow, the distribution of the mean concentration in the cross section changes with time, and  the diffusion coefficient influences the mixing volume in turbulent flow.