Biogas plant managers often face difficulties in obtaining feedstock at stable and affordable prices. The context in which the biogas plant manager needs to purchase the feedstock could be important when the biomass is also used in valorization trajectories besides anaerobic digestion. Using a combination of qualitative research and agent-based modelling, we investigated the effect of market context on the purchase of local biomass for anaerobic digestion. This paper details the institutional arrangements of our case study, the silage maize market in Flanders and the results of a scenario analysis, simulating nine different market contexts. Silage maize is an interesting case study, as it is both used for feed by farmers and as an input in biogas plants. The results show that mainly the time of entry into the market explains the difficulties in obtaining a stable supply of silage maize to biogas plants. Furthermore, we found a silage maize price increase for farmers in competition with a biogas plant, especially in case of a silage maize deficit in the market. The different institutional arrangements used have no significant effect. Our findings may guide biogas plant managers in assessing and reducing the consequences of the establishment of a biogas plant, competing for local biomass resources.