Simple statistical mechanics models have been assembled into a wide-range equation of state for the hydrogen isotopes. The solid is represented by an Einstein-Gru¨neisen model delimited by a Lindemann melting curve. The fluid is represented by an ideal gas plus a soft-sphere fluid configurational term. Dissociation and ionization are approximated by modifying the ideal gas chemical-equilibrium formulation. TheT=0isotherm and dissociation models have been fitted to new diamond-anvil isotherm and laser-generated shock data. The main limitation of the model is in ionization at high compression. ©2000 American Institute of Physics.