<p>The effect of impermeable seabed undulation is examined on the performance of an oscillating water column (OWC) wave-energy converter (WEC) against oblique incident waves. The multi-domain boundary element method is adopted to address the unknown hydrodynamic coefficients of engineering interest based on the linearized potential flow theory. Various types of seabed geometries such as rectangular bottom elevation (RBE), semi-trapezoidal bottom (STB), and semi-circular bottom (SCB) of impermeable and permeable kind are placed underneath the OWC-WEC, and their effect on the variation of OWC efficiency, radiation susceptance, radiation conductance, and wall-force coefficient is reported and evaluated against the relative wave frequency. The significance of angle of incidence, lip-wall rotation, chamber spacing, undulation height, and porosity on the variation of hydrodynamic coefficients is reported. The behavior of OWC efficiency is observed to be different when compared with other traditional behavior of OWC-WEC under various conditions. The magnitude of fluid resonance is higher after introducing the bottom undulations of the porous kind when compared with the impermeable undulations. The increase of the angle of incidence suppresses the fluid resonance in the chamber region, which leads to the drastic reduction of OWC efficiency. The enhancement of seabed height minimizes the gap region that leads to the enhancement of OWC efficiency for moderate wave frequencies. Finally, the comparative study is reported between all three seabed geometries, like RBE, STB, SCB, etc., with no-bottom undulation, and among them, the performance of OWC with RBE is significant.</p>