The results of a research program are presented where an approximate methjd of calculation has been developed for buckling of thick walled steel tubes. In a relatively simple manner, an upperbound is found for buckling in the plastic range under the action of combined external pressure, axial force and bending moment, including the effects of initial out-of-roundness. By means of this method, designers can fairly quickly gain an insight into the influence of pipe characteristics on buckling, under the action of combined loading.