figure includes fields which are not in the North Sea (onshore, West of Shetland). United Kingdom Continental Shelf production was 137 million tonnes of oil and 105 billion m³ of gas in 1999. (1 tonne of crude oil converts to 7.5 barrels). The Danish explorations of Cenozoic stratigraphy, undertaken in the 1990s, showed petroleum-rich reserves in the northern Danish sector, especially the Central Graben area. The Dutch area of the North Sea followed through with onshore and offshore gas exploration, and well creation. Exact figures are debatable, because methods of estimating reserves vary and it is often difficult to forecast future discoveries. Peaking and decline Official production data from 1995 to 2020 is published by the UK government. Table 3.10 lists annual production, import and exports over that period. When it peaked in 1999, production of North Sea oil was 128 million tonnes per year, approx, 950,000 m³ (6 million barrels) per day, having risen by ~ 5% from the early 1990s. However, by 2010 this had halved to under 60million tonnes/year, and continued declining further, and between 2015 and 2020 has hovered between 40 and 50 million tonnes/year, at around 35% of the 1999 peak. From 2005 the UK became a net importer of crude oil, and as production declined, the amount imported has slowly risen to ~ 20 million tonnes per year by 2020. Similar historical data is available for gas. Natural gas production peaked at nearly 10 trillion cubic feet (280×109 m³) in 2001 representing some 1.2GWhr of energy; by 2018 UK production had declined to 1.4 trillion cubic feet, (41×109 m³). Over a similar period energy from gas imports have risen by a factor of approximately 10, from 60GWh in 2001 to just over 500GWh in 2019. UK oil production has seen two peaks, in the mid-1980s and the late 1990s, with a decline to around 300×103 m³ (1.9 million barrels) per day in the early 1990s. Monthly oil production peaked at 13.5×106 m³ (84.9 million barrels) in January 1985 although the highest annual production was seen in 1999, with offshore oil production in that year of 407×106 m³ (398 million barrels) and had declined to 231×106 m³ (220 million barrels) in 2007. This was the largest decrease of any oil-exporting nation in the world, and has led to Britain becoming a net importer of crude for the first time in decades, as recognized by the