he relationship between the percent of volatile solids (VS) reduction and the gas yield is shown in Table 4. The values for VS destruction indicate that the gas yield in R1 (which contained 100% poultry litter) was lower than R2 and R3 and was higher than R4. Because there was no cow dung in R1 and R4 to stimulate the process with bacteria, poultry litter alone was the major source of biogas in the slurry. Therefore, VS reduction was lower in both reactors. On the other hand, in R2, which contained 25% cow dung and 75% poultry litter, the volatile solids reduction was 51.99%. Although gas production in R3 was lower than in R2, it was comparable, which indicates that VS reduction not only depends on the initial concentration but also on the type of volatile matter in the slurry. The yield of gas generation was higher in R2 than in the other three reactors. These results imply that poultry litter alone is not a suitable option for optimum gas generation.