During normal pressure measurements in flat rolling, conducted in the roll gap of laboratory mills, unexpected multiple pressure peaks appeared. These multiple pressure peaks, such as a double peak, have not only been measured during rolling of billets, but also when rolling slabs or strips. Not explained by the established rolling theory stating just a single maximum point. In order to investigate its physical mechanisms a number of rolling experiments are presented. A model duo mill, load transducers, powder lubrication or by vaseline and wax as model material were used. The normal pressure, the shear stress and its angular movement were measured simultaneously. By first measuring a double normal pressure peak during rolling of a wax specimen and then by consciously making changes in draft, specimen thickness, rolling velocity, specimen width or the friction conditions, respectively, the double peak phenomena were investigated by means of the responding normal pressure distribution. A number of direct measurements in the roll gap by other researchers using different techniques, have also been investigated. The conclusion from the wax rolling experiments and the rewiew of measurements by others is that the peak at entry of contact is caused by the presence of compressive stresses from rigid zones outside the deformation zone, raising the hydrostatic pressure and the normal pressure. The effect is observed by inhomogeneous deformation. The peak value at the entry of contact can then be very high, by analogy to plane indentation with elastic regions present. The resistance of the wax material to the height deformation of the specimen was seen to increase at small reductions or by a specimen with a greater nominal thickness, supporting the rigid end theory. The result of this study is also that the exit peak in the double peak is caused by frictional surface stresses at the roll/specimen interface. The effect was seen by changes in frictional influencing factors, such as the reduction or the surface friction condition. Lateral spread of the material rolled was at the same time seen to make the double peak more distinct, decreasing the normal pressure in the valley between the two peaks and at exit of contact.