This report on the third and final stage of the International Collaborative Program concentrates on the analysis of internal and external variability of carbon-14 dates obtained from samples involved in the full carbon-14 dating process. In all, 38 laboratories took part in this stage with most producing eight carbon-14 dates from three sets of duplicate material (e.g. , wood, shell, and peat) and two single samples of wood of known ages 190 years apart. From the three sets of duplicates for each laboratory, the internal precision of most laboratories was adequate; six labs grossly underestimated their internal reproducibility. From the carbon-14 determinations from the five distinct samples for each laboratory, the authors discovered significant systematic biases, often greater than 100 years, in 15 laboratories and even accounting for bias, 12 laboratories had significantly greater external variability than explained by their quoted errors. In total, 23 out of the 38 laboratories in this stage of the study failed to meet these three basic criteria for an adequate performance in the production of carbon-14 dates.