Rough schematic comparing relative dimensions of earth's crustal thickness, depth of the Kola well, and height of Mt. McKinley.
On Russia's Kola Peninsula, near the Norwegian border at about the same latitude as Prudhoe Bay, the Soviets have been drilling a well since 1970. It is now over 40,000 feet deep, making it the deepest hole on earth (the previous record holder was the Bertha Rogers well in Oklahoma--a gas well stopped at 32,000 feet when it struck molten sulfur).
It is not oil or gas that is being sought with the Kola well, but an understanding of the nature of the earth's crust. The United States began a similar investigation, called Project Mohole, in 1961.