Source: EWG analysis of leasing and drilling records in 12 western states, contained in the Bureau of Land Management's Land and Mineral Records 2000 database, acquired by EWG May 15 2004.

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The term "private land" refers to lands for which the surface is owned by a private entity, but subsurface minerals remain in government ownership and can be leased for oil and gas drilling. EWG's estimates of leasing activity on private land are not exact, and are constrained by the resolution of available public land data layers. For leases shown on EWG maps that bound public and private lands, BLM field offices should be contacted for verification on the exact location of the lease relative to public land boundaries.

EWG's estimates of leases that are currently producing oil or gas are constrained by the accuracy of information in BLM's Land and Mineral Records 2000 database, and may represent an overestimate. We have identified cases for which BLM has failed to enter the data necessary to identify particular leases on which production has ceased. An EWG request for more accurate production data is currently being processed by the Department of the Interior.