The performance of a 2-m(3) rubber-balloon biogas plant was evaluated under hilly conditions and compared with a fixed-dome type Deenbandhu biogas plant of the same capacity. The daily average (over one year) biogas production in the rubber-balloon plant was 0.92 m(3)/d, compared to 1.23 m(3)/d in the Deenbandhu plant. The difference in biogas production was 33.7%. A reduction of about 77% was found in the rate of biogas production from the rubber-balloon plant during winter months as compared to production during the summer months. However, the corresponding reduction in production of gas from the Deenbandhu biogas plant was only 16%. The methane contents of the biogas of both the plants were almost identical but the moisture in the gas was 43% higher in the rubber-balloon than in the Deenbandhu plant. The changes in ambient temperature affected the rubber-balloon plant more than they affected the conventional plant.