Wibaux Fire Chief Brian Nelson said Wednesday he is not sure what is in the tanker to keep it burning for five days, and there will be no further attempts to put it out because of the uncertainty.
Fire officials will monitor the fire around the clock until it burns itself out, he said.
Custom Carbon Processing converts waste called slop oil from the oil producing process that would otherwise be discarded and turns it into pipeline-grade oil the company sells to oil buyers.
The facility eight miles outside Wibaux, at the western end of the Bakken oil boom, was a former oil well and then a disposal well. It opened in September as Michels Salt Water Disposal and Oil Reclamation Facility capable of reclaiming slop oil.