Strontium- and magnesium-doped lanthanum gallate (LSGM) was deliberately prepared to give A-site deficient nonstoichiometry with compositions (La0.9Sr0.1)z(Ga0.8Mg0.2)O3-δ (z = 1.0, 0.98, and 0.95). Creep tests in four-point bending for 950 °C < T < 1350 °C and 15 MPa < σ < 75 MPa in air demonstrated that all three compositions shared a common stress dependence, n= 1.49 ± 0.10, and a common apparent activation energy, Q = 426 ± 9 kJ/mol. Despite this agreement, the creep rates of the different compositions depended on grain size in different ways: p = 3.1 ± 0.2 for z = 0.98, and p = 1.9 ± 0.1 for z = 0.95. The measured apparent activation energy, Q, for creep is similar, though statistically significantly smaller, than that measured in another LSGM. Both are nearly twice as large as reported activation energies for cation impurity diffusion. The absolute magnitude of the creep rates, after correction for grain size, were 30 to 100 times slower than in another LSGM of similar composition.