Electron-hole (e−h) compensation is a hallmark of multiband semimetals with extremely large magnetoresistance (XMR) and has been considered to be the basis for XMR. Recent spectroscopic experiments, however, reveal that YSb with nonsaturating magnetoresistance is uncompensated, questioning the e−h compensation scenario for XMR. Here we demonstrate with magnetoresistivity and angle-dependent Shubnikov–de Haas (SdH) quantum oscillation measurements that YSb does have nearly perfect e−h compensation, with a density ratio of ∼0.95 for electrons and holes. The density and mobility anisotropy of the charge carriers revealed in the SdH experiments allow us to quantitatively describe the magnetoresistance with an anisotropic multiband model that includes contributions from all Fermi pockets. We elucidate the role of compensated multibands in the occurrence of XMR by demonstrating the evolution of calculated magnetoresistances for a single band and for various combinations of electron and hole Fermi pockets.