An improved procedure for wet combustion of ₁₄C NBS oxalic acid standard was devised which gives consistent high C yields and an average delta ₁₃C value of -1.91%. The principal cause of fractionation in earlier attempts to prepare CO₂ by the wet oxidation method was the inexact nature of the end point. The new procedure uses a chocolate-brown end point by adding 5 ml more of the H₂SO₄ -- KMnO₄ solution after the initial, reddish-brown end point is reached. The H₂SO₄-KMnO₄ solution is added to the NBS oxalic apparatus, and a cycling technique is used to collect the CO₂. Fifteen samples of the NBS oxalic acid were processed. The C yields range 97.8-100% with an average of 98.8% and an average delta₁₃C of -- 1.912%. The results obtained by this procedure are much more consistent than previous results obtained by direct combustion. See <i>AATA 17-865. -- AATA