In collaborative ontology engineering, contexts are key to manage the complexity of different dependency types between ontological artefacts. Instead of being frustrated by out-of-control evolution processes, proper context dependency management will allow human experts to focus on the meaning interpretation and negotiation processes. This requires support for the detection and resolution of meaning ambiguities and conflicts. In this article, we explore to which extent the theory of graph transformation can be used to support this activity. More specifically, we propose the use of critical pair analysis as a formal means to analyse conflicts between ontologies that are evolving in parallel. We illustrate this with an example from a realistic case study.