A detailed C-13-NMR procedure has been developed to analyze ethylene-propylene-rubbers (EPM). Special attention has been paid to instrumental and spectral parameters and calculation methods. By applying this procedure, it is possible to obtain consistent and reproducible molecular composition results on EPM, independent of the measuring laboratory and the calculation method. The procedure has been tested in eight industrial laboratories. Using this procedure, the composition of a set of 10 EPM standards has been defined. These standards will be used for worldwide infrared calibration purposes (ASTM D-3900).