The in situ stress field was determined at a depth of 837 m (2745 feet) in Devonian Shale ('gray' shale) within the Rome Basin in West Virginia. Logging data and laboratory observations of core samples reveal vertical cracks oriented at N50¿-60¿E. Because of these cracks and their preferred orientation a new approach based on fracture mechanics concepts is used to evaluate the in situ stresses from the field and laboratory data. The resulting prediciton of the maximum horizontal stress (&sgr;Hmax) is compared to the maximum horizontal stress predicted by Haimson and Fairhurst's (1967) method; the latter method appears to overestimate the value of this stress component because the effect of loading the faces of any preexisting crack is neglected.