The 5:27 p.m. EDT blast and fire occurred in the Reynolds Industrial Park near Greenville, about 80 miles northwest of Pittsburgh, the Pittsburgh Tribune-Review reported.
The tank belonged to Brownies Oil Co., a division of Reed Oil Co., the Pittsburgh Post-Gazette said.
Mary Kress, 54, told the Post-Gazette she heard the explosion and saw a "ball of flames." She said the tank hit a tree, bounced and landed near her home.
Gary Clark, a spokesman for the state Department of Environmental Protection, said investigators were trying to determine whether the explosion may have been sparked by a welder working about 300 feet away from the above-ground tank. He said victim was believed to have been the welder.
The Tribune-Review said company officials could not be reached for comment.