North Dakota regulators say a cow is suspected of causing a spill of natural gas liquids near a tributary of the Little Missouri River.

The North Dakota Department of Health says a cow may have rubbed against a tank valve on Tuesday, spilling about 20 barrels of natural gas condensate near Sully Creek, in western North Dakota.

Condensate is a byproduct of natural gas production.

The agency says the site is owned by a subsidiary of Oneok Inc. based in Tulsa, Oklahoma. Regulators say cleanup is under way and booms have been put in Sully Creek as a precaution.

Neither the company nor regulators immediately returned calls seeking comment Thursday.