Very few in situ lunar sulfur studies exist, with the major focus being on bulk-rocks in which a relatively restricted sulfur isotope fractionation is observed, leading to suggestions that the source of sulfur in the lunar interior is homogeneous. Using a novel approach, we present for the first time two complementary datasets combining in situ secondary ion mass spectrometry and X-ray absorption near-edge structure spectroscopy of lunar apatite, to investigate the late-stage behaviour of sulfur in lunar basaltic melts. Our measurements reveal varied sulfur contents of ~20–2,800 ppm and δ34S values of -33.3 ± 3.8‰ to +36.4 ± 3.2‰ (2σ). The apatites have S6+/ΣStot ratios of >0, with average values as high as 0.55, providing evidence for the existence of relatively oxidized late-stage silicate melts on the Moon. We propose the existence of multiple, previously unrecognised, distinct sulfur isotopic reservoirs in the lunar interior and atypical oxidizing conditions in late-stage silicate melts. These findings are important for our understanding of lunar formation processes and the evolution of redox conditions during the formation of terrestrial bodies.