Abstract: This work presents a review of the ideas that are currently in use on the ontology-based conceptual modeling of occurrents (sometimes referred to as “events”, “perdurants”, or “processes”). It collects such ideas from a set of 11 ontologies, which includes some of the most important and widely used upper ontologies (i.e., BFO, UFO, DOLCE, YAMATO, SUMO, GFO). We analyze the ontologies with respect to the definition of occurrent they present and their understanding about participation, mereology, and causation. The commitments regarding these four facets of occurrents are gathered in three categories (pervasive aspects, complementary aspects, and conflicting aspects). Additionally, we identify the main occurrent classification criteria used to branch the taxonomy of the ontologies. These findings are summarized in two tables at the end of the paper, which may be used by modeling practitioners as reference. The review shows that the considered ontologies agree in a significant set of common aspects as well as present some relevant divergences. However, there is a considerable set of non-conflicting, complementary aspects scattered among the diverse ontologies. It suggests an opportunity for efforts aiming to harmonize those views in a single approach that may enrich the analysis and representation of occurrents.