In accordance with the Waste Incineration Directive (WID), it is compulsory that a co-incineration plant is checked annually by a specialist or an expert institution for representative compliance with requirements. In the context of such inspections, the samples from nine different waste suppliers have been taken in compliance with standards (ÖNORM 15442) given for solid recovered fuels. Afterwards, chemical and physical analyses were performed at the Laboratory for Environmental Analysis at the University of Leoben (Montanuniversität). The wastes types under investigations were classified into Hot Disc (HD) material (larger particle size) and Main Burner (MB) material. Special emphasis was laid on the calculation of the minimum sample amount. It was calculated from the maximum particle diameter d95 in accordance with the standard ÖNORM 15442 – annex F. For a better material fraction characterization of wastes, sieving and sorting analyses were performed. Such, the exact composition and the particle size distribution of investigated wastes could be identified. Finally, the results were compared and discussed. At the end of the thesis, a mathematical model for the plant dependent enrichment curves of waste fractions is explained.