The Land and Mineral Use Records web site is an Internet mapping application within NILS' GeoCommunicator. It allows users to search, locate, and map the BLM's land and mineral use authorizations and mining claims on public lands throughout the United States. Land and mineral use authorizations include such things as oil and gas leases, rights-of-way, mineral leasing, coal leasing, unpatented mining claims, withdrawals, classifications, and land and mineral title.
Here's another site that I think is a good resource. In 2004, Environmental Working Group did a report titled "Who Owns the West?" The link is to the section on oil & gas leases. Obviously, the Bush administration has done more in the last four years.