We extend the Open WordNet for English (OWN-EN) with rock-related and other lithological terms using the authoritative source of GBA’s Thesaurus. Our aim is to improve WordNet to better function within Oil & Gas domain, particularly geoscience texts. We use a three step approach: a proof of concept-level extension of WordNet, a major extension on which we evaluate the impact with positive results and a full extension encompassing all GBA’s lithological terms. We also build a mapping to GBA which also links to several other resources: WikiData, British Geological Survey, Inspire, GeoSciML and DBpedia.