Bi12SiO20and Bi12GeO20present the best known photorefractive sensitivity for read‐write volume holographic storage (S−1≃300 &mgr;J/cm2) combined with high‐quality image reconstruction. Recording processes by photocarrier diffusion (no applied field) and by photocarrier drift are identified. The high photosensitivity is attributed to photocarrier displacements comparable to or larger than fringe spacings. Saturation diffraction efficiency at light power densities larger than 600&mgr;W/cm2at &lgr;=514.5 nm occurs from complete photocarrier trap filling.