Electrical submersible pumping (ESP) is an artificial lift system used in the petroleum industry. ESP skid is an equipment in which the pump is housed inside a pipe forming a slightly inclined annular duct through which two‐phase gas–liquid flows from inlet to pump intake. Part of the gas is pulled by the pump and part is separated and flows to the equipment top. This article analyses and models the observed separation process. Experiments showed good qualitative but poor quantitative agreement with literature models. Starting from a two‐dimensional drift‐flux model, radial and axial slips are modeled through phases' momentum transfer, showing the importance of drag, virtual mass and Basset's forces, leading to a semi‐analytical model. As there is no model for such forces for the case of annular duct in the literature, experimental data is used for closure. The proposed model produced satisfactory and physically coherent results.