Oil produced in the North Sea. A combination of advances in oil technology and the rise in oil prices in the 1970s led to a dramatic rise in UK-based oil production. Output rose from approximately nil in 1973 to a level equal to 9 percent of productive sector output by 1979. This dramatically improved the UK's balance of payments: in 1974 net imports of fuel were equal to 3½ percent of gross domestic product (GDP), while in 1983 net exports of fuel were equal to 4 percent of GDP. Production of North Sea oil peaked in 1999 and has fallen since. It is expected to fall to a third of the peak output by 2020.