Regulators with the state Oil and Gas Division say Houston-based Oasis Petroleum North America reported the 470-barrel spill on Wednesday at the well near White Earth. A barrel is 42 gallons.
Officials say the spill was caused by a failed fitting that caused a tank to overflow. A state inspector has been on site investigating the spill.
North Dakota Department of Mineral Resources spokeswoman Allison Ritter says no water sources were affected.
Saltwater is an unwanted byproduct of oil production and is considered an environmental hazard by the state. It is many times saltier than sea water and can easily kill vegetation exposed to it.