The Renewable Energy Source Act (EEG) promotes German biogas production in order to substitute fossil fuels, protect the environment, and prevent climate change. As a consequence, green maize production has increased significantly over the last years, causing negative environmental effects on soil, water and biodiversity. In this paper we quantitatively analyse the EEG-reform in 2012 by applying the simulation tool ReSI-M (Regionalised Location Information System – Maize). Comparing the EEG 2012 with a former version of the legislation, results imply that the reform leads to reduction of biogas electricity generation compared to former versions, and thus to less substitution of fossil fuels. Furthermore, given a restriction in the share of green maize input, its production is reduced and the crop-mix is diversified. However, since maize provides the highest energy output per area, total land requirement for biogas production increases. An alternative analysis shows that an EEG with tariffs independent from plant-types would provide the highest subsidy efficiency, but slightly lower land efficiency compared to the EEG 2012.