The Ghawar field, discovered in 1948 in Saudi Arabia, is the largest oil field in the world; it measures 174 by 19 miles and is located in the eastern area of Saudi Arabia near the Persian Gulf. It accounts for more than half of the cumulative oil production of Saudi Arabia. Ghawar is entirely owned and operated by Saudi Aramco, the state run Saudi oil company. Saudi Aramco's value has been estimated at anywhere between US$1.25 trillion and US$7 trillion, making it the world's most valuable company. Saudi Aramco has the world's largest proven crude oil reserves, at more than 260 billion barrels. Its 2013 crude oil production totaled 3.4 billion barrels from 100 oil fields.
(Adapted from ‘The Handy Science Answer Book, compiled by the Science and Technology department of the Carnegie Library of Pittsburgh; and from Wikipedia encyclopedia)