Nectar is the principal floral visitor reward offered by plants and the volume and sugar concentration determine its energetic value. We report how nectar secretion and sugar concentration determine energy variation for Eriotheca gracilipes on first and second day flowers under two Cerrado physiognomies (cerrado and campo cerrado). We found great variation for both sugar concentration and nectar production rate on the flowers of E. gracilipes, and nectar production rate is the best predictor of energy content on flowers. Most nectar was produced during the first day flowers and three times more nectar was secreted during the male than female phase. This 3:1 ratio in nectar production could match the higher number of Anthophoridae bee visits required to saturate male vs. female functions. Energy production per flower differed among individuals for male phase flowers and among patches for female phase flowers. These variations in spatial scales could influence the bee foraging behaviour. We consider the possibility that these sexual traits are under sexual selection (Grant from CNPq 141472/2003-0).