WILLISTON – An investigation is continuing into the cause of an oil-field explosion northwest of Williston Friday.

According to the North Dakota Department of Mineral Resources, gases released from the oil well led to the explosions and fire, although the source of ignition is unknown.

The incident occurred during well intervention with a workover rig shortly after 6 p.m. at the East Fork site operated by Grayson Mill Operating. The fire was contained to the well and workover rig and remained on the constructed well pad. Minimal fluids were released and all appeared to be consumed by the fire, which eventually was extinguished, the incident report stated.

Of the five workers at the site, three sustained injuries and ultimately were transported to a burn hospital in Colorado.