The analysis of the mechanism of air leakage through the interstices between metal surfaces in contact or of the mechanism of thermal resistance between them is dependent on the average clearance between opposite surfaces or on the distribution of the real contact area; i.e., the mechanism of contact. Assuming that the distribution curve obtained from the profile curve of the surface has a normal distribution, the relation between the applied load and the average clearance or the penetrating depth, i.e., the distance through which the one surface moves into the other surface, is obtained theoretically. A comparison of calculated values based on this theory with experimental data shows good agreement.