The high-accuracy W4 computational thermochemistry protocol, and several post-W4 methods, have been applied to the P2 and P4 molecules. Contrary to previous studies, we find the experimental thermochemistry to be fundamentally sound. The reaction enthalpy for P4 ! 2P2 has a very significant contribution from post-CCSD(T) correlation effects. We derive a gas-phase heat of formation for the phosphorus atom of H f, 0½PðgÞ ¼ 75:54 0:1 kcal mol1 and H f, 298½PðgÞ ¼ 75:74 0:1 kcal mol1, in the upper half of the CODATA uncertainty interval.