The largest oil and natural gas producer in the EU, the United Kingdom retains proven crude oil reserves of around 4 billion barrels and proven natural gas reserves of some 18.8 Tcf as of 2006. Containing the bulk of domestic reserves and an extensive network of subsea pipelines and infrastructure, the UK Continental Shelf (UKCS) is the most active offshore region for the UK's oil and gas sector, and industry giants Shell, ExxonMobil, Chevron and Total all explore and produce there. The third largest global energy company and headquartered in the UK, BP is operator of such major offshore UK producers as the Foinaven and Forties fields.