In the local Universe, the e ffi ciency for converting baryonic gas into stars is very low. In dark matter halos where galaxies form and evolve, the average e ffi ciency varies with galaxy stellar mass and has a maximum of about 20% for Milky-Way-like galaxies. The low e ffi ciency at higher mass is believed to be the result of some quenching processes, such as the feedback from active galactic nuclei. We perform an analysis of weak lensing and satellite kinematics for SDSS central galaxies. Our results reveal that the e ffi ciency is much higher, more than 60%, for a large population of massive star-forming galaxies around 10 11 M (cid:12) . This suggests that these galaxies acquired most of the gas in their halos and converted it into stars without being significantly a ff ected by quenching processes. This population of galaxies is not reproduced in current galaxy formation models, indicating that our understanding of galaxy formation is incomplete. The implications of our results on circumgalactic media, star-formation quenching, and disk galaxy rotation curves are discussed. We also examine systematic uncertainties in halo-mass and stellar-mass measurements that might influence our results.