Requirements managers aim at keeping the set of requirements con-sistent and up to date throughout the project by conducting the following tasks: requirements categorization, requirements conflict analysis, and requirements tracing. However, the manual conduct of these tasks takes significant effort and is error-prone. In this paper we propose to use semantic technology as founda-tion for automating the requirements management tasks and introduce the on-tology-based reporting approach OntRep. We evaluate the effectiveness and ef-fort the OntRep approach based on a real-world industrial empirical study with professional Austrian IT project managers. Major results were that OntRep pro-vides reasonable capabilities for the automated categorization of requirements, was when compared to a manual approach considerably more effective to iden-tify conflicts, and produced less false positives with similar effort.