One eyewitness described the fire at Eco-Oil Ltd at the Kingsnorth Industrial Estate at Hoo as "huge".
Kent Fire and Rescue Service managed to contain burning oil which spread on to adjacent land cleared for development.
Firefighters said the blaze started at about 2300 BST and was finally brought under control at around 0545 BST.
The fire started in two road tankers before spreading to plastic and steel drum oil containers.
No casualties have been reported.
At least 10 fire crews from around the county were tackling the fire, with extra foam units brought in from London and Essex.
Graham Gash, area manager from Kent Fire and Rescue said: "Crews have done a great job in fighting this serious fire and successfully managing to prevent it spreading further and damaging nearby buildings.
"We worked alongside our partners from the London Fire Brigade and Essex Fire and Rescue Service and I think praise goes to everyone for a job well done."
Mr Gash said crews were confronted by a very serious fire involving road tanker vehicles carrying 1,000-litre containers of reclaimed engine oil and numerous 200-litre barrels of oil which were exploding.
He added: "More importantly, we had fuel that was flowing from the site and this posed a significant threat to the surrounding building which was three industrial units."
The fire officer said foam had to be used to put out a very hot oil fire, while two high volume water supplies were needed for a major foam strike - one for cooling and one for foam production.
He added: "This particular area is not very well served with a good water supply so we had to run in two water mains from Kingsnorth power station."
By about 0800 BST on Saturday, fire crews had entered the turning over and damping down phase, Mr Gash said.
He said crews were working to make sure the fire was out and checking the industrial units with thermal imaging cameras to make sure there had been no undetected fire spread.
Mr Gash said there was minimal risk to people nearby because the industrial estate was surrounded by commercial industrial retail outlets and not residential areas.
He said the brigade's fire investigation team would be investigating the cause of the fire along with Kent Police.

The Air Accidents Investigation Branch (AAIB) also said emergency workers had to delay their response because some explosive cartridges were still live.
Its report said the seats were a "significant hazard" that delayed rescue teams until they were made safe.
The Hawker Hunter jet plummeted on to the A27 on 22 August killing 11 men.
A final report is still to be published by the AAIB, but seven safety recommendations have been made in the bulletin, which has looked at the safety of ejection seats and the maintenance of ex-military aircraft.
The AAIB said manufacturer support for the jet had ended after it was retired from military service, and its technical manual had not been updated.
The explosive cartridges for the jet's ejector seat and canopy had expiry dates of June and July 2014, more than a year before the crash.
Sussex Police said officers were at the scene immediately after the crash and the issue of the ejector seats arose when victim recovery was taking place and the aircraft had to be lifted.
The AAIB report also said investigators could not determine if the aircraft met the requirements of its permit to fly from December 2014 onwards.
Aircraft that do not qualify for a standard certificate of airworthiness - generally former military or amateur-built planes - are able to operate with a permit to fly granted by the Civil Aviation Authority (CAA).
But the AAIB report revealed that initially the CAA "could not determine" if the Hawker Hunter met the requirements of its permit, because of doubts over the validity of the maintenance of its Rolls-Royce engine.
It recommended the CAA review its procedures over issuing such permits to ex-military aircraft.
A CAA spokesman said it was examining the AAIB bulletin in detail, but stressed it did not contain any information about the cause of the crash.
He said the CAA had told the AAIB investigation the jet had a valid maintenance record at the time of the crash.
"The aircraft did have a valid permit to fly at the time of the accident and was therefore permitted to operate," he added.
Work had been carried out on the aircraft in January 2014 and the next inspection was due in January 2016, the CAA said.
The AAIB said investigations would continue and it was still examining the aircraft and its maintenance records to determine its exact condition before the accident.
Pilot Andy Hill has been interviewed by police, it was confirmed last week.
More than 60 firefighters have spent the night tackling a major blaze at a waste oil depot near Kingsnorth power station in Kent.
[NEXT_CONCEPT]
A jet that crashed during the Shoreham air show, killing 11 men, had expired ejector seat parts and an out-of-date technical manual, a report has said.