Query: What types of companies existed in a few major oil and gas production centers?
Context: The upstream tended to be far more centralised with much of the technical and financial direction coming from the central offices in The Hague. Nevertheless, there were very large "exploration and production" companies in a few major oil and gas production centres such as the United Kingdom (Shell Expro, a Joint Venture with Exxon), Nigeria, Brunei, and Oman.