A quantitative C-13 nuclear magnetic resonance analysis of an ethylene-propylene copolymer produced on a modern high-field instrument produces a spectrum with eight discrete groups of peaks. Assignment of these peaks provides eight simultaneous equations to describe the six triad distribution numbers. We have demonstrated the advantages of solving directly this over-determined set of equations. We have observed that the relative uncertainty in the different triad numbers is approximately constant, and have used this observation to discuss the uncertainties in individual triad numbers as a function of their concentration.