The partial electronic conductivities (sigma(el)) of La0.9Sr0.1Ga0.9Mg0.1O2.90 (LSGM9191), La0.9Sr0.1Ga0.8Mg0.2O2.85 (LSGM9182) and La0.8Sr0.2Ga0.8Mg0.2O2.80 (LSGM8282) were measured by Hebb-Wagner ion-blocking method between 700 and 900 degreesC. As the Sr and Mg content increases, both the hole and the electron conductivity decrease together with the increasing activation energy of conduction. The electronic transference numbers of the three compositions were approximately 10(-2) similar to 10(-3), much larger than that of zirconia. From the Hebb-Wagner curves, the variation of sigma(el), was obtained as a function of oxygen partial pressure (P-O2). The thermal band-gap energy (E-g) value was estimated from the conductivity minima. The possible sources of error in estimating E-g were discussed. E-g value was much smaller than that of yttria-stabilized zirconia (YSZ).