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According to the latest data from the U.S. Energy Information Agency, in 2011, U.S. E&P companies saw a 15% increase in proved reserves during 2011, adding nearly 3.8 billion bbl of crude oil and lease condensate, Table 1. This jump, to a 29.0-billion-bbl total, marks the largest annual increase since the agency began publishing such estimates in 1977. In the wet natural gas arena, U.S. proved reserves rose to an all-time high of 334.07 Tcf, representing a gain of 29.44 Tcf. Only one year, 2010, saw a higher annual increase than 2011, when operators added 33.8 Tcf.
| Table 1. U.S. crude oil and lease condensate proved reserves, reserves changes and production, 2011, MMbbl. |
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This rising activity was driven, in part, by the increased use of new drilling technology to extend reserve profiles in difficult-to-tap formations, including shales. Crude oil prices hovering near $100/bbl also contributed to increased drilling and development activity, in preparation for future production at higher crude prices.
In fact, the assumption that oil prices will continue to rise is considered an influencing factor in the increase of estimates among EIA respondents, because operators are considering a larger swath of their resource bases economically producible.
The most recent jump in estimated oil and gas reserves marks an increase in the importance of domestically-produced hydrocarbon resources in fueling current, and projected, domestic demand. And, as U.S. production and reserves levels rise, reliance on imports has shown a slight, but notable, decline. For EIA’s purposes, proved reserves are those that are considered to have an assumed probability of recovery of 90%, or higher, as shown through geological and engineering data analysis.
In taking stock of total reserves, estimates are driven higher by new discoveries, the re-appraisal of existing fields, the production of existing reserves, and changes in pricing and technological abilities. In the tables referenced here, discoveries comprise new fields, new reservoirs in previously-discovered fields and extensions of estimated reserves in given reservoirs, through further drilling and exploration. According to the EIA, these extensions tend to make up the largest percentage of total discoveries per year, although more fanfare may be directed at new finds. The greater portion of reserves additions is most often the result of operators re-estimating their ability to produce existing properties.
Crude and condensate. In each of the country’s five largest crude and condensate areas (Texas, federal Gulf of Mexico, Alaska, California and North Dakota), proved reserves increased during 2011. Perennial high producer Texas added roughly 1.8 billion bbl, accounting for the largest individual area increase, and 47% of the net increase for the U.S. North Dakota followed in second place, adding 771 million bbl, for 20% of the net increase. These states represented two-thirds of the net growth, and saw gains driven by development in the Permian, Western Gulf and Williston basins.
Proved oil reserves gains were dominated by an uptick in activity in tight oil plays, especially in North Dakota’s Bakken and Three Forks formations. More than 90% of domestic tight oil reserves for 2011 were found in the four largest plays of that kind: Bakken, Eagle Ford, Barnett and Niobrara.
Natural gas. Across Texas, Wyoming, Louisiana, Oklahoma and Pennsylvania, E&P companies increased wet natural gas reserves during 2011, led by Pennsylvania’s 90% increase (to a statewide total of 26.5 Tcf), Table 2. Together, Pennsylvania and Texas contributed 73% of the net increase in domestic gas reserves. Increases were buoyed by continuing Marcellus formation and Appalachian basin development, along with expanding shale activity elsewhere in the U.S.
| Table 2. U.S. dry natural gas proved reserves, reserves changes and production, 2011, Bcf. |
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EIA continues to catch up on its reserves reporting, and intends to release its next tabulation in March. 
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