Data integration and knowledge representation in the oil and gas drilling domain are two challenges much work is focused upon. They are important real-world challenges to deal with, and the drilling domain has much to gain from better solutions than the ones that exist today. Data integration is a problem that has been known for a long time, but the existing solutions are cumbersome and expensive to use and maintain. Ontology based data integration is one approach that shows much promise and is currently gaining ground. This thesis presents both necessary theoretical background, and also domain knowledge that serves as important input. With the insight gathered from this background, an ontology for the drilling domain is created, and two use cases that are based on this ontology are presented. One of these cases is a general description of a data integration case using the QuOnto framework, and the other is a XML to RDF data conversion tool created in Java.