Steady-state multiaxial creep equations that may be applied to the analysis of nonlinear and volume-nonconservative in-reactor creep data have been derived. Strain rate equations are expressed in terms of the stress exponent, n, a rate constant, B, and a material parameter, β. Equivalent stress states are assumed to give equal mechanical energy dissipation rates, and the associated equivalent stress and plastic strain rate criteria are shown to be functions of both the shear and hydrostatic components of the stress and strain-rate tensors, respectively. The deviatoric creep rate coefficient is shown to be an apparent function of stress state when swelling is stress dependent and the stress exponent is greater than unity. The possible magnitude of this stress-state effect is estimated for fast-neutron-irradiated austenitic stainless steel using available microstructural models.