A mixture of 125Sb, 154Eu, and 155Eu has been used to prepare gamma-ray emission-rate standards with a functional life of over 10 years and with useful photon emissions at over 18 energies between 25 and 1600 keV. The standards are useful for the calibration of the efficiency of germanium gamma-ray detectors in this energy range. Correlated summing corrections are moderate, compared to many radionuclides which provide multiple calibration points. Photon-emission rates for the major radiations have been measured, for sources quantitatively related to the standards, with four germanium spectrometer systems especially calibrated for the purpose. For two coaxial detectors, efficiency values were established at 28 energies between 88 and 2800 keV, with an average total uncertainty, estimated at a level corresponding to a standard deviation of the mean, of about 0.6%. At lower energies, the most reliable calibration points were given by X- or gamma-rays directly measured with defined-geometry NaI(Tl) systems. Calculated efficiency curves were used for interpolation between these points. Significant efficiency changes of the coaxial detectors with time were monitored and accounted for. The emission rates of selected X-rays and gamma-rays from the standards are specified with total uncertainties of from 0.6% to 1.3%, estimated to correspond to one standard deviation of the mean.