A series of 30.4 by 10 by 1.6-cm tensile panels of an API SLX-70 pipeline steel with different surface crack lengths and depths were tested. Measured crack-mouth-opening displacements (CMOD) were compared with the predictions from linear elastic fracture mechanics (LEFM) plus the modified critical crack-opening displacement (COD) model. Within the range of crack sizes and shapes studied, good agreement between the experimental data and the predictions from the LEFM plus the modified critical COD model was observed. Surface deformations observed in the neighborhood of the crack also are discussed. The surface deformation patterns were obtained through instrumentation of the specimen with electrical resistance strain gages and brittle lacquer. On the front surface of the specimen, the deformation patterns revealed by the brittle lacquer correlated well with the observed CMOD-stress relations. The highest strain regions on the back surface were about ± 45 deg from the plane of the crack emanating from the leading edge of the crack. The ligament yielding stress estimated from the modified critical COD model agreed well with the readings of the electrical resistance strain gages on the back surface.