Biomethane potential (BMP) tests are a valuable tool to design different parts of full-scale anaerobic digestion plants. Recent inter-laboratory studies have shown that the results of BMP tests can vary considerably and a comparison of BMP test norm protocols showed that the procedures are not rigorously defined, thus leaving room for interpretation. The goals of the present study were to develop a test protocol based on the existing ones but defining all steps precisely and to test the influence of the origin of the inoculum and its adaptation to the test substrate. The results showed that the amount of methane produced per gram of substrate volatile solids added varied only slightly with the different inocula used and that adaptation to the substrate did not increase the methane production from complex substrates. The reproducibility of the tests was good and tests with cellulose showed a methane production close to the theoretical methane yield. Future efforts will be directed to the comparison of BMP estimations with biogas production of full-scale installations from the same organic substrates.