In this paper, acid wormholing in carbonate formations is studied. The wormhole growth rate and the geometry of the final worm-hole pattern depend on the combined effect of acid spending and fluid flow. Acid spending is studied by modeling the wormhole as a cylindrical pore and numerically solving the convection-diffusion equations. A finite acid-rock reaction rate is assumed, allowing calculation and study of spending profiles in both the diffusion-controlled and the reaction-controlled regime. Flow properties such as fluid loss from wormhole to formation and fluid distribution in a multiple wormhole geometry are studied through numerical simulations. It is shown how wormhole growth properties are affected by the length and distance of neighboring worm-holes. The effect of injection rate and diffusion is studied with a simple model. This model explains several experimentally observed phenomena, such as the existence of an optimum injection rate and a reduced wormhole efficiency at higher rates.