The bond characteristics of four different types of glass fiber reinforced plastic (GFRP) reinforcing bars with different surface deformations were analyzed in experiments. Local bond stress-slip data, as well as bond stress-radial deformation data, needed for constitutive modeling of the interface mechanics, were obtained for varying levels of confining pressure. In addition to bond stress and slip, radial stress and radial deformation were considered fundamental variables needed to provide for configuration-independent relationships. Each test specimen consisted of a #6 GFRP reinforcing bar embedded in a 76-mm (3-in)-diameter, 102-mm (4-in)-long cracked concrete cylinder subjected to a controlled, constant amount of confining axisymmetric radial pressure. Only 67 mm (2.6 in) of contact was permitted between the bar and concrete. For each reinforcing bar type, bond stress-slip and bond stress-radial deformation relationships were obtained for five levels of confining axisymmetric radial pressure. The researcher found that small surface indentations were sufficient to yield bond strengths comparable to that of steel bars. Effects of deformations on tensile properties were discussed. It was noted that radial pressure is an important parameter that can increase the bond strength threefold.