The wet mass methane potentials for the substrates listed in Table 1 are displayed graphically in Figure 2. Wet mass methane potential is highly dependent on solids content. The wet mass methane potential of the covered pen beef manure sample (14 m3 CH4 per 1,000 kg wet weight) is seven times that of liquid swine manure slurry (2.0 m3 CH4 per 1,000 kg wet weight), even though the specific methane yield of swine manure is slightly higher (0.13 liters CH4/g VS) than beef manure (0.10 liters CH4/g VS). The major difference between these two samples is the beef manure tested contains 17 percent TS and the swine manure contains only 2.6 percent TS. The more concentrated beef manure produces more methane per wet mass than the dilute swine manure. Wet mass methane potential is a good standard by which to size up co-digestion products. There is no point in