The problem of oblique water wave diffraction by three asymmetrically arranged vertical porous barriers with different widths in infinitely deep water is investigated. Reflection and transmission coefficients are evaluated, applying single-term Galerkin approximation. The amount of energy loss is derived employing Green's integral theorem. Wave force is determined using the linear Bernoulli equation of dynamic pressure jump, on the porous barriers. Forces and energy of the wave are studied to understand the effect of the dissipation of wave energy due to the presence porous barriers. Numerical results for the reflection coefficient, wave force, and wave energy dissipation are analysed graphically. The comparison of the numerical results are carried out for the validity of the derived solution. It is observed that porosity affects significantly on reflection coefficient and amount of energy dissipation. It is also found that more energy is dissipated if the permeability of the barriers is increased. © 2020 Informa UK Limited, trading as Taylor & Francis Group.