The application of process mining techniques to real-life information systems is often challenging. Considering a Purchase to Pay (P2P) process, several case notions such as order and item are involved, interacting with each other. Therefore, creating an event log where events need to relate to a single case (i.e., process instance) leads to convergence (i.e., the duplication of an event related to different cases) and divergence (i.e., the inability to separate events within the same case) problems. To avoid such problems, object-centric event logs have been proposed, where each event can be related to different objects. These can be exploited by a new set of process mining techniques. This paper describes OCEL (Object-Centric Event Log), a generic and scalable format for the storage of object-centric event logs. The implementation of the format can use either JSON or XML, and tool support is provided.