The biochemical methane potential (BMP)) assay was evaluated in terms of inoculum (rumen versus primary sludge digester), inoculum-to-feed ratio, and particle size for analysis of extent and rate of conversion of biomass and waste feedstocks to methane. The rumen and sludge inocula exhibited similar solubilization of particulate matter. An inoculum-to-feed ratio of 2:1 was shown to give maximum conversion rates. Particle size did not influence rate in the range of 1-8 mm. An extensive data base on the biochemical methane potential of several biomass and waste feedstocks is presented, including freshwater, marine, herbaceous, and woody feedstocks and municipal wastes; data for plant parts are also included. In addition, the influence of several parameters on the BMP of feedstocks are presented, including growth and harvest conditions, and ensiling.