To clarify the sealing characteristics of metal gasket seals, leakage rates of gas and the real contact area of the seal surfaces were measured under several closing loads. The static seal consisted of a ring-shaped copper gasket and the two steel flanges that held the gasket in place. Gasket widths in the radial direction were 2 mm, 3 mm, and 5 mm. The contact surfaces of the flanges were finished by lathe turning. To determine the leakage flow paths between the gasket and the flanges, the real contact situation between them was observed using a thin polymer film in thickness. The results indicated the leakage flow paths on the gasket surface were the radial direction perpendicular to the lathe-turned groove and the circumferential direction along the groove. As the closing loads increased, the leakage flow in the radial direction ceased and only that in the circumferential direction remained. Therefore, the cross-section of the aperture for the leakage flow in the circumferential direction was evaluated from the measured real contact area, and the leakage rates were estimated by assumption of laminar flow. The results agreed well with the measured leakage rates.