In magnetic fields of up to 50 kOe and at T = 4.2 K, the field dependences of the magnetore-sistance of pure tungsten single crystals with a residual resistance ratio p293K/p42K of about 75000 under the static skin effect, i.e. the concentration of direct current near the conductor surface, were measured. The size effect, i.e. the dependence of the magnetoresistance on the dimensions and shape of the sample as well as the direction of the magnetic field relative to its surface, was studied. It was shown that under these conditions the conductivity (resistivity) near the sample surface is several orders of magnitude higher (lower) than that in the conductor bulk. Using the trivial formulas, it is possible to "separate" the contributions of the bulk and surface conductivities. A similar method can be used to estimate the contributions to the bulk and surface conductivities of more complex systems with an inhomogeneous distribution of electric current across the conductor cross-section