There were no reports of injuries and no immediate evacuations ordered in this south-central Oklahoma town, said Mike Hancock, a spokesman for Wynnewood Refinery Co.
"Tank fires are pretty pesky fires. They're easy to keep contained, but they're hard to fight," Hancock said. "It's hard to estimate how long it will be. It can take a day or so to burn the product."
Firefighters continued to douse the area surrounding the tanks to keep the iron from overheating, Hancock said.
One tank contained about 50,000 barrels of naphtha, an unrefined form of gasoline, and the second tank contained about 30,000 barrels of diesel fuel, Hancock said.
"They each had quite a bit of product," he said.
The initial fire began around 11:45 a.m. when lightning from a cluster of thunderstorms hit the tank containing naphtha, police Chief Ken Moore said late Friday.
Fire crews from Wynnewood and the refinery owner sprayed foam on the fire and transferred some of the naphtha out of the tank following the first fire.
But hours later, an apparent explosion was heard by residents from communities several miles away, and both tanks became involved.
Hot naphtha from the first tank spread to another tank, igniting a fire near the second tank, which contained diesel fuel, sending flames and smoke hundreds of feet into the air, officials said. Moore said an explosion could have been caused by the collapse of the first tank.
"As the fire grew hotter and hotter, parts of the original tank collapsed. This allowed some of the (naphtha) to flow out and flow around the second tank," Moore said.
Authorities closed U.S. Highway 77 between Oklahoma Highway 29 and State Highway 17A for most of the day as a precaution, Moore said. A road on the south side of the refinery also was closed.
Moore said the nearest homes were within a quarter-mile of the refinery.
Power to the refinery, which is a division of Denver-based Gary Williams Corp., also was shut down, Hancock said.
"Electric power feeds near that tank, and the heat was starting to effect the power poles," Hancock said.
The fire is the second at the facility, which produces gasoline, diesel fuel, military jet fuel, solvents and asphalt, in less than two years.
A blaze in May 2006 in the refinery's alkylation unit led to the evacuation of 150 nearby residents. An acid leak a week later related to fire damage caused more evacuations.
The Occupational Safety and Health Administration issued 22 violations over that incident.
The refinery processes about 50,000 barrels of oil a day and employs about 185 people.
Wynnewood is about 65 miles south of Oklahoma City.