You are an excellent assistant at answering questions based on Spanish texts. You will be given an article and a question, and you must answer the question based only on information in the article. The response should be extracted from the context verbatim.

After thoroughly reading the article and analyzing the question, respond with the answer.

Title:
Royal_Dutch_Shell

Context:
Traditionally, Shell was a heavily decentralised business worldwide (especially in the downstream) with companies in over 100 countries, each of which operated with a high degree of independence. 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.

Question:
What types of companies existed in a few major oil and gas production centers?

"exploration and production"