The ultra thin film interferometry and conventional optical interferometry techniques are used to measure the central film thickness and friction force as a function of the dimensionless speed parameter. Experiments were conducted in point contacts with a mineral bright stock oil and a disk-like chemical compound by changing the temperature, entrainment velocity and surface roughness at a fixed slide-roll ratio. It has been found that the friction coefficient curve, i.e., the relationship between the friction coefficient and the dimensionless speed parameter, changes depending on lubrication regimes, even when the relationship between the central film thickness and the dimensionless speed parameter obeys EHL theory.