Quick reference pages
For quick reference on sector terms, there is a Glossary of Upstream Terms, a A Glossary of Petroleum Refining Terms and A Glossary of LNG Terms
For those of you who want to know the difference between Brent & WTI, the Crude Oil Types page will be useful. There is also a section on Unconventional Oil and Gas Resources .
An Introduction to Refining section, gives the basics of how refining works.