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Copaiba trees, of the genus Copaifera (Fabaceae), produce an oleoresin that has pharmacological applications. The yield from the trees is very variable, and factors affecting production are still unknown. We evaluated the yield of oleoresin from Copaifera spp. in the Cerrado–Amazonia ecotone, as well as its relationship with the growth and age of trees. We sampled 30 Copaifera trees by extracting oleoresin for 24 h with a metal borer. Wood cylinders were collected from 15 trees to determine their age by counting growth rings and to calculate the mean annual increment of the diameter at breast height. The cylinders were sanded and the number of growth rings was counting with a magnifying glass (10x). The ages of trees from which wood cylinders were not collected were estimated by simple regression analysis. The proportions of productive and non-productive trees were recorded. The best adjusted model for age estimation showed R²adjust. = 0.616 and Syx% = 4.42. The average productivity of oleoresin was 0.124 L, and 30% of the trees were productive. The proportion of productive trees increased with increasing diameter at breast height and age, but after a point, increasing diameter was associated with reduced productivity. The mean annual increment had an inverse relationship with diameter. Thus, in the primary forest, only copaiba trees at an advanced age produce oleoresin; however, the trees become unproductive when they reach senescence. Plans for the sustainable harvest of this resource should take these factors into consideration.