February 2001
Special Focus

United States: U.S. reserves

Oil & gas reserves up, but not from new fields

Feb. 2001 Vol. 222 No. 2 
Outlook 2001: United States 


Oil & gas reserves up, but not from new fields

U.S. proved crude oil reserves increased a healthy 3.5% to 21.8 billion bbl in 1999 – the largest increase since EIA began tracking reserves some 23 years ago. Prices, which roughly doubled during the year, were the most important factor responsible for the increase.

Total dry gas discoveries (sum of extensions, new fields and new reservoirs in old fields) were down 5% in 1999 – 10% from the past 24-year average. However, gains in revisions and adjustments more than offset that decline, yielding a net gain of about 2% for 1999.

Crude oil. Proved reserves additions replaced 137% of crude production in 1999, again, mostly due to price increases. Texas and California – which account for 43% of U.S. crude reserves – saw increases of 412 and 91 million bbl, respectively; while Alaska and the federal Gulf of Mexico – which together comprise 36% of crude reserves – had 152 and 49 million bbl reserve decreases, respectively.

Total discoveries of crude were 725 million bbl, 21% higher than discoveries made in 1998. Chief among those was 423 million bbl discovered in the federal GOM, which was 58% of the national total. Although discoveries were up from 1998 levels, 1999 saw 4% fewer discoveries than the average of the past 10 years.

New field discoveries were 321 million bbl – 44% of total discoveries. Overall, reserves from new field discoveries were 74% more than the prior 10-years’ average. Extensions accounted for 259 million bbl (36%), while new reservoirs in old fields were 20% of total discoveries.

For the past two decades, crude oil reserves have been largely sustained – or rather, held to an average slow decline of 500 million bbl a year – by extending and developing existing fields. Also called Proved Ultimate Recovery Appreciation, its largest components are revisions and adjustments, which account for 62% of all crude reserves additions. Since 1976, only 8% of added reserves were from new field discoveries.

Natural gas. Proved dry gas reserves stood at 167.4 Tcf at year-end 1999, and operators replaced 118% of dry gas production, which increased 1% during the year. Added to gas reserves were 22.3 Tcf – 43% more than in 1998, excluding production.

The three largest increases were in: Texas, 2,573 Bcf; Colorado, 1,106 Bcf; and Utah, 825 Bcf. The three biggest losing areas were: federal GOM offshore Louisiana, – 1,176 Bcf; Oklahoma, – 1,102 Bcf; and Kansas, – 649 Bcf.

Coalbed methane development in the San Juan basin, together with conventional gas discoveries / revisions, were responsible for Colorado’s additions. Utah’s increase was primarily due to coalbed methane development in the Uinta basin. Nationally, coalbed methane production rose another 5% in 1999, to 1,252 Bcf – about 7% of U.S. dry gas production.

Wet-after-lease-separation gas reserves increased about 2.2% to 176,159 Bcf (these include dry gas reserves plus NGLs before they are stripped out). Wet gas reserves have two components: non-associated gas, which improved 2.1%; and associated gas, which gained 2.5%.

Reserves of NGLs increased 5% to 7,906 million bbl. Operators replaced 143% of NGL production with reserve additions in 1999. NGLs account for 27% of total liquid hydrocarbon reserves (NGLs + crude reserves), which are at 29,671 million bbl – 4% more than in 1998. WO

Go Estimated U.S. crude oil reserves, 1999 vs. 1998, million bbl
Go Estimated U.S. dry gas reserves, 1999 vs. 1998, Bcf at 14.73 psia and 60°F
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