The Environment Web (EW) is the official database for emissions and discharges from the offshore oil and gas industry in Norway. Currently we are working on a project to describe and align terms in the EW application according to the ISO 15926 Reference Data Library (RDL). One of our goals is to ensure that the EW terms in the RDL can be used as a reference point for all systems using EW terms. Therefore the definitions of the EW constructs in the RDL need to be unambiguous. Moreover, another goal is to enrich the ISO 15926 ontology by adding terms from the EW domain.We briefly describe our experiences and challenges faced so far when mapping terms from the EW database to the ISO15926 Ontology.