Oxide-based memory devices are an active research area due to complementary metal−oxide−semiconductor compatibility and recent dramatic increases in their performance and endurance. Many atomistic aspects of their operation are driven by the interplay between electronic and ionic processes, the mechanisms of which are still poorly understood. Recently a mechanism of electroforming process based on the formation of oxygen vacancies (VO) and interstitial O ions facilitated by electron and hole injection into the oxide has been proposed for SiO2 and HfO2 based devices [1]. Here we provide an atomistic insight into the transport of oxygen vacancies and interstitial oxygen ions, Oi, from the bulk of amorphous SiOx and TaOx, films to interfaces with TiN electrodes in the context of electroforming and performance of TiN/SiOx/TiN and TiN/TaOx/TiN devices, where x characterizes the degree of oxide reduction. In the case of SiOx, we extend the description of the bulk Oi2− migration to the interface of amorphous SiOx with the polycrystaline TiN electrode, using density functional theory (DFT) simulations. In the bulk of SiOx, interstitial migration is rapid and nondirectional in the absence of any external bias, with migration occurring in accordance with the interstitialcy mechanism [1]. In the presence of the external bias, the diffusion becomes directional, with the Oi being moved from the bulk toward the interface. At the interface, the incorporation and migration barriers for the Oi become vanishingly small, introducing a strong thermodynamic and kinetic driver for the transport of Oi to the interface. The arrival of Oi2− at the interface is accompanied by preferential oxidation of undercoordinated Ti sites at the interface, forming a Ti−O layer. [2]. We then investigate how Oi ions incorporate into a perfect and defective Σ5(012)[100] grain boundary (GB) in TiN oriented perpendicular to the interface. Our simulations demonstrate the preferential incorporation of Oi at defects within the TiN GB and their fast diffusion along a passivated grain boundary [2]. We demonstrate that in the case of TaOx, it is the hole injection that facilitates the formation of VO2+ vacancies and interstitial Oi atoms. The latter bind to Ti at the TiN interface and can be released upon bias application similarly to the SiOx/TiN case. These results explain how, as a result of bias application and carrier injection, the system undergoes very significant structural changes with the oxide being significantly reduced, interface being oxidized, and part of the oxygen leaving the system. The bias application facilitates the carrier injection into the oxide; these extra electrons or holes reduce energy barriers for the creation of O vacancies, and these barriers as well as those for O ion diffusion are further lowered by the field.