The aim of the paper is to estimate effect of nonuniform thickness of the fouling layer on its thermal resistance. To do this, series of numerical experiments have been carried out for several assumed shapes of the fouling layer. Span of the work involves four different nonuniform shapes and a reference case of the uniform thickness, either with the same deposit mass. The effect has been demonstrated by ratio of the fouling thermal resistance for shapes of nonuniform deposit to the reference case of uniform layer. Modes of heat transfer taken into considerations are convection, radiation and combined convection and radiation from the hot gas to the foulant outer surface. The results clearly suggest that the fouling thermal resistance depends essentially on the shape. Consequently, if fouling would be allowed to occur at the tube outer periphery, then the thermal resistance resulted from can be mitigated significantly by fouling layer shaping.