Fibrous-bed coalescers are commonly used to separate oil-in-water emulsions, and some factors significantly affect the separation performance. To achieve a fundamental understanding of the colloidal physical phenomenon and to predict the coalescence efficiency are challenging tasks because of the complex interplay among the governing parameters. Here, two types of commercial oleophilic fibers were employed to study the influence of critical factors on the separation performance, including the packing density, the specific surface area, the bed depth, the superficial velocity, and the inlet oil content. An industrial-scale experiment was also carried out on an offshore platform. The collected industrial data will be useful to further the application of the oleophilic-fiber bed in oily wastewater treatment.