The permeation of an oil-in-water emulsion through a coalescing filter is studied numerically. Our simulation model is based on the phase-field model owing to its simple description of the wetting behavior of oil droplets on versatile surfaces. To realize two-dimensional (2D) simulations of the coalescing processes, we construct a 2D filter model which describes the cross-sectional structure of a fibrous filter in a simple manner. We investigate the effects of wettability, permeation flux, and fiber diameter on coalescing behavior. Oil droplets attach to the fibers and coalesce with each other, forming a bridging structure between fibers which promotes droplet coalescence unless the bridging structure blocks the entire flow path. This coalescence-promoting effect of the bridging structure is observed under conditions where the fluid velocity inside a pore is relatively large. We demonstrate that our numerical model provides useful information to effectively design a coalescing filter and process. (c) 2016 American Institute of Chemical Engineers