Due to its high value of dielectric strength, oil is often used for transformer insulation. Nevertheless, its presence needs to be considered when determining thermal coordination of a converter system, which also includes the challenging modeling of fluid dynamics. This paper presents an analytical model for calculation of oil temperatures and average flow velocities inside vessels that contain both oil and windings of a medium frequency transformer. The verification of the developed analytical model is performed based on a small-scale experimental setup. The paper demonstrates that the analytical model reasonably agrees with the selected verification method, and can aid design optimization.