The fire was reported shortly after 1 p.m. Friday at PBF Energy's Delaware City Refinery in the 4500 block of Wrangle Hill Road.
Black smoke could be seen from several miles away.
The view from Chopper 6 showed flames shooting out of a building with firefighters pouring water on the blaze.
Refinery officials say all workers have been accounted for. No injuries have been reported.
The fire was placed under control at 3:17 p.m.
PHOTOS: Fire at Delaware City refinery
The fire was reported to be inside a catalytic cracker. It's described as a "a chemical reactor for converting oils with high boiling points into fuels with lower boiling points in the presence of a catalyst."
From the refinery's website:
The Delaware City refinery is located on a 5,000-acre site on the Delaware River, with the ability to accept crude by rail or waterborne cargoes. Delaware City possesses an extensive distribution network of pipelines, barges and tankers, truck and rail for the distribution of its refined products.