The impact of oil in Alaska

alaska's basement is rich in oil gas, coal, gold zinc and others ores. But above all, this state guarantees 17 % of the American production of petroleum : 90 % of the alaska's budget comes from hydrocarbon.
The north of the state, also called North Slope constitutes an important stock of petroleum, particularly harnessed ( = exploited) by companies like British Petroleum, Exxon, or Arco. It is called National Petroleum Reserve.
oil is also exploited in off-shore (in the sea) despite difficult climatic conditions. Prudhoe Bay area affords half of the Petroleum in alaska: 400 000 barrels a day, which represents 8% of the American production.