Deep knowledge of two-phase oil-water flow behavior through horizontal pipelines is crucial for transportation network design. In particular, the behavior of core annular flow (CAF) pattern where oil flows as the core fluid and water flows as an annular fluid. A three-dimensional model of transient isothermal flows in a horizontal pipe was created using CFD code ANSYS FLUENT 2020 R1 applying an explicit Volume of Fluid (VOF) scheme. CFD simulation study was performed on heavy oil-water CAF flow and validated with the experimental study. CAF pattern was determined during numerical runs conducted at various mixture superficial velocities. Thicker eccentricity core flow has been observed numerically and consistent with the flow visualization observed experimentally. The interfacial waves appeared in the simulation study during the flowing due to Kelvin-Helmholtz instability. The simulated oil holdup and transient pressure were found to be in reasonable agreement level with Areny's holdup correlation predictions and experimental results, respectively. This investigation further demonstrates that the CFD model may predict the hydrodynamic behavior of CAF to a satisfactory level.