Three theories - the time-hardening theory, the strain-hardening theory, and the life-traction theory - are investigated in an effort to predict creep strains under conditions of varying loads from data obtained at constant load in the range of interest to the structural designer. A method is presented for computing an equivalent rupture stress for the varied load case using the lite-traction theory and the rupture curve tor constant stress tests. The analytical methods are compared with data obtained from 2024-T3 aluminum-alloy sheet under tensile creep at constant and varying loads.