Chromia forming Alloy 718 and AD730™ have been submitted to isothermal long-term air exposure up to 10 000 h at 700 °C. The resulting very low specific mass gain led to consider two alternatives to determine the oxidation kinetics. Measurements of the external layer thickness and of the intergranular oxide amount were carried out on SEM micrographs evidencing the intergranular oxidation contribute around 30% to the total specific mass change. AD730™ with a thicker external scale and a higher amount of intergranular oxide showed a twofold faster oxidation rate than Alloy718. The results demonstrated the need of even longer tests.