The purpose of this work was to examine the tensile strength of coke and to relate this to fissure formation in industrial coke. The tensile strength was determined using the diametrical-compression test, the test specimens being obtained from half-oven-width lumps by drilling cores from a series of positions across the lumps. Strain gauges were used to determine the critical breakage strain of selected samples and the results in conjunction with apparent density values were considered in the light of current knowledge of the relation between breakage and structure as it refers to fissure formation in coke. The results demonstrated that the tensile strength of industrial coke varies widely, across half-oven-width lumps, among individual lumps, and among different cokes. Although the tensile strength of coke is sensitive to changes in apparent densin/ there is no generally applicable correlation. Within the limitation that extrapolation of the results is necessary in order to obtain data for the semicoke which is of significance in fissure formation, it is considered that fissure formation is probable if the tensile stress developed within the semicoke during carbonization exceeds 3.5 MN/m*; the strain developed must be in excess of 2 X 10-3. * or other lumps in the case of the sample from the commercial coke sample D, which contained no such pieces