The solute strengthening effect of oxygen in commercial-purity Zircaloy-2 was investigated over the temperature range 1023 to 1873 K, strain rate range 10⁻⁴ to 10⁻¹s⁻¹, and oxygen concentration range 1260 to 12 360 ppm. The flow parameters were determined in the fully α and fully β as well as (α + β) phase domains. In the two-phase region, the flow curves were characterized by significant yield drops as long as the β volume fraction was over about 50 percent. This effect is ascribed to the enrichment of the β-phase in the substitutional solutes iron and possibly chromium. The flow curves were otherwise normal. For the single-phase α and β structures, the yield and steady-state stresses obeyed the general relation σ = σ₀ exp (kc), where σ₀ and k are constants, and c represents the oxygen concentration (weight percent). The average values of k_α and k_β were determined to be 0.57 ± 0.06 and 0.34 ± 0.10, respectively. The strain rate sensitivities fell in the following ranges, depending on the phases present: 0.15 to 0.20, 0.27 to 0.32, and 0.22 to 0.25 for the α, β, and (α + β) materials, respectively. The experimental activation energies decreased with stress in the ranges 450 to 330 kJ/mol (50 to 150 MPa) and 150 to 120 kJ/mol (1 to 5 MPa) for the α- and β-Zircaloy-2, respectively. The extrapolated zero stress values of Q were 530 and 170 kJ/mol, and are associated with the dominant dynamic recovery mechanism in each phase. The observed steady-state as well as yield stresses correspond closely to the rule-of-mixtures predictions but lie considerably above the values interpolated from the fully α-phase and fully β-phase. This is ascribed to the very powerful strengthening effect of oxygen on the α-phase when it is enriched during the formation of two phases from either single-phase region.