There is a growing interest on Open Source Enterprise Resource Planning (OS-ERP) systems among organizations today. When developing ERP systems a major problem is requirements management. Proponents of open source development often claim it has a high level of involvement from users in adopting organizations. However, comparing with proprietary ERP development it is not that clear if users are more or less involved in OS-ERP development. User involvement in ERP requirement management is problematic and it makes development a complex endeavour. One problematic area is about identifying and selecting requirements for future development. In this paper we explore how requirements engineering is done in the OS-ERP area. To do this, we use a theoretical base on requirements management in the ERP field from which we investigate how requirement engineering in development of four different OS-ERP systems is done. The basic question asked is: How are requirements engineering done in Open Source ERP development. From the investigation we present a general picture of the requirements management process in the OS-ERP area. The main conclusion is that the requirement engineering in OS-ERP development does not differ a lot from proprietary ERP development, for example regarding end-users involvement it is found that they are not involved to the extent first expected and when comparing with proprietary ERP development a similarity regarding requirements engineering in both types of ERP development was discovered.