OSHA has already began an investigation but do not yet know the cause in an oil well explosion near Watford City Saturday.
One man was killed and three others injured, two critically.
The McKenzie County Sheriff’s Department says 52-year-old Johnny Stassinos of Rock Springs, Wyoming, died Saturday afternoon from injuries suffered that morning at a well site operated by XTO Energy Inc. east of Watford City.
28-year-old Daniel Montes of Fruita, Colorado, and 27-year-old Richard Maheu of Rock Springs, Wyoming, were airlifted to the Regions Burn Center in St. Paul, Minnesota, where they were listed in critical condition. 
Authorities say 40-year-old Justin Pyle of Grand Junction, Colorado, was treated for minor injuries at a Watford City hospital and later released.
XTO Energy is a subsidiary of ExxonMobil. 
A spokeswoman says the men were contractors working for companies that do maintenance on oil wells when the explosion happened.