Dedicated to Prof. Dr. Eckard Kratzig on the occasion of his 60th birthday.Five annealed BaTiO3:Rh crystals, including as-grown and those reduced at 10-5 atm, 10-10 atm, 10-12 atm, and 10-14 atm oxygen partial pressures, were produced and investigated by two-beam coupling at wavelengths of 514 nm and 633 nm. The carrier type is a function of reduction degree and incident wavelength. The compensation points are around 10-3 atm and 10-11 atm oxygen partial pressures for 514 nm and 633 nm, respectively. The electrooptic gain is controlled by the photoconductivity–dark conductivity ratio, effects from the deep and shallow traps, and hole–electron competition, which are dependent on the reduction degree and incident wavelength.