The Greeley Tribune reports there were no injuries in the incident Wednesday about 20 miles south of Greeley.
Television video showed a column of smoke rising from the site.
Jolene Schneider of the Platteville-Gilchrest Fire Protection Agency says about 3,000 gallons of fuel burned.
Ron Gusek of Liberty Oilfield Services says the fire was in a truck equipped to pump water. He says the fire department is investigating the cause.
Noble Energy, which operates the site, says Gusek’s company was preparing a well to begin production when the fire broke out. Noble spokeswoman Paula Beasley says no wells were producing oil or gas there at the time of the fire.