The world of ontology development is full of mysteries. Recently, ISO Standard 15926 ("Lifecycle Integration of Process Plant Data Including Oil and Gas Production Facilities"), a data model initially designed to support the integration and handover of large engineering artefacts, has been proposed by its principal custodian for general use as an upper level ontology. As we shall discover, ISO 15926 is, when examined in light of this proposal, marked by a series of quite astonishing defects, which may however provide general lessons for the developers of ontologies in the future. Keywords. Upper-level ontology, data models for the oil and gas industry, ISO. Forthcoming in B. Bennett and C. Fellbaum (Eds.), Formal Ontology and Information Systems, (FOIS 2006), Baltimore November 9-11 2006, in press. What Happens When Data Models and Ontologies are Confused Ontologies are, in one respect at least, comparable to telephone networks: they are designed to support exchange of inform...