We report experimental and theoretical results on the lateral wet oxidation of bidimensional thin aluminum-rich layers into AlOx. We introduce a reaction-diffusion model of oxidation front propagation that includes effects of anisotropies and compare it to experimental results. This model can be used with any starting geometry, possibly nonconvex, and is deduced from the chemical reactions of wet oxidation of AlxGa1-xAs -based layers. Numerical simulations performed with simple and complex geometries are in excellent agreement with the experimental observations. Our method is general and can apply to other oxides. It opens the way to the fine control of wet-oxidation fronts and to the formation of AlOx layers with a desired geometry that has numerous practical and relevant applications for, e.g., waveguiding or carrier confinement in photonics.