Prudhoe Bay in Alaska, the largest US oil field in 2009, fell to third place, also behind the Spraberry trend area of Texas. Rounding out the top 10 oil fields are Wattenberg in Colorado, Briscoe Ranch, Kuparuk River in Arkansas, Thunder Horse in the Gulf of Mexico, Wasson in Texas, Belridge South in California, and Atlantic in the Gulf of Mexico.
The US overall in 2013 had 36.5 billion bbl of crude oil and lease condensate proved reserves, up from 22.3 billion bbl in 2009. The top 100 US oil fields represented 56.4% of the 2013 total and 62.3% of the 2009 total.
The Marcellus area, meanwhile, discovered only in 2008, ascended to the top spot among the top 100 US natural gas fields, surpassing the Barnett in Texas. The Marcellus, which produced 2.8 tcf in 2013, encompasses proved reserves from north-central West Virginia and the southwest corner to the northeast of Pennsylvania.