The interaction of oblique water waves with a land-fixed Oscillating Water Column (OWC) type wave energy converter is examined. Two-dimensional linear wave theory is used to formulate the mathematical problem. The matched eigenfunction expansion method (EEM) using dual series relations and the Boundary Element Method (BEM) with quadratic elements are utilized to solve the associated boundary value problem (BVP). The novelty of the present work lies on addressing the influence of oblique water waves on the OWC efficiency and the use of dual series relations to solve this type of BVP. Variations of the hydrodynamic efficiency with the wave angle of incidence, and with the chamber length and front barrier draft to water depth ratios are discussed. Both analytical and numerical results were found to be in good agreement. Findings revealed that by increasing the angle of incidence, a broader hydrodynamic efficiency band and a higher wave frequency at which resonance occurs are both obtained. This aspect may offer benefits to wave power extraction in real sea conditions for fixed OWC devices. Finally, cases published in the specialized literature were recovered and very good agreement was achieved.