All literature vibration-rotational and pure rotational transition energies for the ground X1∑+ electronic state of H35Cl, H37Cl, D35Cl, and D37Cl, along with the entire collection of electronic B1∑+ → X1∑+ emission data for the four isotopomers, have been used in a least-squares fit of compact analytic Born-Oppenheimer potential functions for the B1∑ and X1∑+ electronic states. Additional functions related to the adiabatic and nonadiabatic corrections have also been determined. Separate least-squares fits were made according to the hamiltonian operators of J. K. G. Watson (J. Mol. Spectrosc. 80, 411 (1980)) and R. M. Herman and J. F. Ogilvie (Adv. Chem. Phys. 103, 187 (1998)). The results from the separate analyses demonstrate clearly that the two hamiltonian operators are essentially equivalent, both achieving equally satisfactory representations of the spectral data, and furnishing virtually identical Born-Oppenheimer potential functions. Fully quantum-mechanical vibrational eigen-values and rotational perturbation series parameters Bv-Ov are presented for the lower levels of the X1∑+ ground state for which infrared and/or microwave data are available (v″ < 7 for H35Cl and H37Cl, v″ < 10 for D35Cl and D37Cl). These parameters collectively reproduce the corresponding spectroscopic line positions included in our fit to within the uncertainties of the measurements.