The largest deposits in the world occur in the United States in the Green River Formation, which covers portions of Colorado, Utah, and Wyoming; about 70% of this resource lies on land owned or managed by the United States federal government.
Najveće nalazište u svijetu nalazi se u Green River Formationu, koji pokriva dijelove Colorada, Utaha, i Wyominga; oko 70% ovog resursa leži na zemlji koju posjeduje i kojom upravlja Američka federalna vlada.