  We present a theoretical study of the superconducting gap function in
PrOs4Sb12 using a symmetry-based approach. A three-component order parameter in
the triplet channel best describes superconductivity. The gap function is
non-degenerate and the lower branch has four cusp nodes at unusual points of
the Fermi surface, which lead to power law behaviours in the density of states,
specific heat and nuclear spin relaxation rate.
