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Understanding how defects in solids interact with external electric fields is important for technological applications such as memristor devices. Using Density Functional Theory (DFT) calculations, we have studied the influence of an external electric field on the formation energies and diffusion barriers of surface and subsurface oxygen vacancies at the (101) surface of anatase TiO2. DFT in the generalized gradient approximation as well as DFT+U methods with different U values have been utilized, with the electric field treated self-consistently by adding a sawtooth-like potential to the bare ionic potential. Our results show that the direction and strength of the applied field can have a significant influence on the relative stabilities of surface and subsurface defects, whereas the effect on the subsurface-to-surface defect migration is found to be relatively minor. [ABSTRACT FROM AUTHOR]