Fiber-based coalescers are widely used in the chemical industry to separate two immiscible fluids. Due to the complex structure inside a coalescer and the opaque nature of the fiber material, it is impractical to perform direct visualization and measurement of the multiphase flow inside a coalescer. One fundamental problem in understanding the physics inside a liquid-gas coalescer is to determine the maximum size of a drop that can attach and remain on a fiber. Previous studies (Hung and Yao, 1999; Lorenceau et al., 2004; Wang and Desjardins, 2018) have provided models to estimate the maximum size of a drop on a horizontal cylindrical fiber under gravity or cross-flow. However, it is not clear whether these models hold when the fiber shape and contact angle change. In this paper, we numerically investigate the critical drop size on a thin fiber with different shapes and contact angles, and provide a model that can be used for future coalescer modeling and design. (C) 2018 Elsevier Ltd. All rights reserved.