BP is the largest Oil producer in the UK, with 26 fields producing a total of 471,600 bbl/d in 2004, according to OGJ. BP also operates the single-largest oil field in the UK, Schiehallion, with 2004 production of 98,900 bbl/d. Other large oil producers in the UK include Shell, ChevronTexaco, and Total. As UK oil fields mature, the industry has shifted focus from discovering new reserves to increasing the productivity of existing fields and developing smaller, previously avoided ones. This trend has prompted oil major such as BP and Shell to begin selling their UK assets in order to focus on high growth, international opportunities. The result has been the entry into the UK oil sector of many smaller operators. In 2003, U.S.-based Apache purchased BPs Forties field for $630 million, and other smaller operators, such as Talisman, Perenco, and Paladin Resources, have acquired significant production assets in the country. In late 2004, EnCana announced that it would sell its North Sea assets to Canada-based Nexen for $2 billion. In 2005, Denmarks Maersk Oil and Gas and UK Natural Gas company Centrica purchased the North Sea assets of U.S.-based Kerr McGee for $3 billion. These companies find smaller and maturing fields more economically viable than do the oil majors, because they have lower overhead costs, are more flexible, and often employ newer production and recovery technologies.