A C++ algorithm was used to metallurgically design high-performance GMAW electrodes for joining HSLA-65 steel. The electrode design was based on: (1) a carbon content £0.06 wt.% for improved weldability, (2) a 5-15% lower A r3 transformation temperature than HSLA-65 steel for enhanced strength and toughness, and (3) a desirable range of carbon equivalent number (CEN) for consistently overmatching the minimum specified tensile strength of HSLA-65 steel. The algorithm utilized a set of boundary conditions that included calculated A r3 , B S , B F , and M S transformation temperatures besides CEN. Numerical ranges for boundary conditions were derived from chemical compositions of commercial HSLA-65 steel, substituting thermomechanical effects with weld solidification effects. The boundary conditions were applied in evaluating chemical composition ranges of the following three prospective welding electrode specification groups that offered to provide £0.06 wt.% carbon, a minimum transverse-weld tensile strength of 552 MPa (80 ksi), and a minimum CVN impact toughness of 27 J at -29°C through -51°C (20 ft lbf at -20°F through -60°F) in the as-welded condition: (1) ER80S-Ni1, (2) E90C-K3, and (3) E80C-W2. At £0.06 wt.% carbon, the algorithm returned over 3100 results for E90C-K3 that satisfied the boundary conditions, but returned no acceptable results for other two electrode specification groups. Results revealed that welding electrode designs based on an Fe-C-Mn-Ni-Mo system, containing 0.06 wt.% C, 1.6 wt.% Mn, 0.8 wt.% Ni, and 0.3 wt.% Mo that provide weld metals characterized by an A r3 of 690°C, a CEN of 0.29, and a (B F -M S ) of 30°C are expected to consistently overmatch the minimum specified tensile strength of HSLA-65 steel while offering a minimum CVN impact toughness of 41 J at -40°C (30 ft lbf at -40°F).