Additionally, as of 2005, there are more than 260,000 natural gas stripper wells in the lower 48 states. Together they account for over of natural gas, or about 7 percent of the natural gas produced in the lower 48 states. Stripper wells are more common in older oil and gas producing regions, most notably in Appalachia, Texas and Oklahoma.
When marginal wells are prematurely abandoned, significant quantities of oil remain behind. In most instances, the remaining reserves are not easily accessible when oil prices subsequently rise again: When marginal fields are abandoned, the surface infrastructure - the pumps, piping, storage vessels, and other processing equipment - is removed and the lease forfeited. Since much of this equipment was probably installed over many years, replacing it over a short period should oil prices jump upward, is enormously cost prohibitve. Oil prices would have to rise several times higher than their historic highs and stay at elevated levels for many years - before there would be sufficient economic justification to bring many marginal fields back into production.
As a result, once a marginal well is abandoned, the oil that remains behind is often effectively lost forever. Estimates are that the marginal wells plugged and abandoned between 1994 and 2003 represented of crude oil reserves. Although the situation is less severe for natural gas, as of 2005 there is nonetheless a growing concern about the premature abandonment of gas stripper wells. As of 2006, the United States would have to import an additional of oil every day (an increase of 7%), and of natural gas (an increase of 38%) without the aggregate production from its stripper wells.