Steady laminar natural convection flow in a cylindrical enclosure with an aspect ratio (height to radius) of unity has been analyzed numerically for 102≤ Ra ≤2 × 105. The enclosure consists a cold bottom wait and hot side and top walls. Physical geometry and boundary conditions were made to simulate the presence of oil storage tanks in the petroleum industry and passive solar heating for energy-efficient buildings. The flow field is found to consist of two large recirculating zones, both of which are symmetrical. Results indicate that a major fraction of the total heat transfer comes from the bottom wall. The Prandtl number effect is also presented for 1 ≤ Pr ≤ 200.