Numerical flow visualization was made on air contained in parallelogrammic thermal enclosures under various angles of gravitational fields for enclosure aspect ratio of 3.0. Rayleigh numbers considered are in the range of 103 to 106. The gravitational fields act on the enclosures in angles varying from 0° to 360° in steps of 15°. For air with a Prandtl number of 0.7, a transition in the mode of fluid circulation was observed when the gravitational field is varied and the mean Nusselt changed from maximum to minimum. Flow visualization experiments were made for air with Pr≅0.7 at Ra≅ 2x105 with aspect ratios of the order ≥ 1.