Precisely machined tensile specimens of aluminum-killed steel sheet were used to measure the continuous strain-rate sensitivity,m c, in a series of isothermal tests at different crosshead speeds.m cwas found to be independent of strain and strain rate, in contrast with the “jump” test instantaneous strain sensitivity, mi, which was found to vary strongly with strain rate. A series of matched tensile specimens was also photogridded and deformed at three rates and terminated at four elongations. The strain distributions obtained from these tests were compared with Finite Element Modeling (FEM)—calculated ones based on several strain-rate sensitivity formulations. Comparison of calculations with experiments revealed that the operant rate sensitivity during tensile localization,m t, was intermediate betweenm candm iat each rate and elongation. Once the effective rate sensitivity was established, detailed predictions of strain distributions and failure elongations agreed very well with experiment. A qualitative model of strain-based stress transients was proposed for both strain-rate and strain-state path changes.