Base metal technology, mainly using Ni electrodes in multilayer ceramic capacitors (MLCCs), is now well established. This technology requires a so-called reoxidation treatment after sintering the MLCCs in a reducing atmosphere to guarantee a sufficient electrical reliability. Large numbers of electrodes, and production of physically larger components for high-voltage components, are two technological trends that make the control of the reoxidation process rather difficult. The reoxidation process has been studied to determine oxygen diffusion pathways into commercial MLCCs, using O-18 tracer diffusion and finite element calculations. In MLCCs oxygen diffusion mainly occurs along the Ni electrodes. Furthermore, the reoxidation process is mostly controlled by the thermodynamic potential of the Ni/NiO equilibrium in the interior of the capacitor, but it is the short circuit diffusion along the interface of the electrode that controls the kinetics of the oxygen transport into the interior of the capacitor device.