Three bodies have been recovered so far from the site, and mop-up operations are under way.
"Body of one more person was recovered this afternoon. While, two persons, whose bodies were recovered earlier, have been identified, we are trying to identify the third," Surat District Collector Jayprakash Shivhare told PTI.
"All the three persons, who perished in the fire, are not regular, but contractual employees," he said.
The fire has been completely brought under control after more than 24 hours, he said.
"However, the entire operation may continue for some more time. Till the Controller of Explosives tells us that chances of another fire is not there, we will continue our operation," Mr Shivhare said.
The incident is likely to force the country's largest refiner to import fuel.
Officials say the victims were inside the storage facility when the fire broke out.
Oil Minister Veerappa Moily, who visited the spot earlier today, said a high-level investigation into the incident has been ordered and a report is expected by January 20.
Mr Moily appreciated the work of local administration, fire brigade and other public and private sector companies for the massive disaster management operation and containing the fire.
He said petrol worth Rs 35 crore has been burnt and another Rs 10 crore loss of infrastructure has also been reported in the blaze.
The minister announced on behalf of IOC a compensation of Rs 5 lakh each to the kin of those who died in the incident.
"We have already ordered a high-level investigation into the matter and the report is expected by January 20," he told reporters after visiting the site.
"It is under investigation whether the fire was caused by human error or not, both by the district administration and a high-level inquiry. Everything will be investigated. No one will be spared if there is an error," he said.
"The fire has been contained. Even though the other tanks were situated just by the side of Tank No. 4, the damage was controlled and contained. The fire was confined to only one tank," Mr Moily said.
"When we got a fire call in one of the petrol tanks of IOC terminal here yesterday afternoon, fire experts opined that the crucial thing would be to contain the blaze from spreading to other storage tanks while allowing the petrol in the tank number four to burn out," Mr Shivhare said.
The tank where the blaze started had about 5,000 kilolitres of gasoline, almost half of IOC's capacity, when it caught fire.
"Because of wind the fire has spread to another petrol tank. We can see smoke coming out of second petrol tank as well. It had substantial volumes," said N Srikumar, executive director at the company.
Mr Srikumar had said earlier that IndianOil was looking into the cause of the fire that broke out on Saturday afternoon.
IndianOil, which meets about half of the country's domestic fuel demand, along with its subsidiary, Chennai Petroleum, control 10 refineries accounting for about 31 per cent of the national capacity of 4.3 million barrels per day (bpd).
This is the second major fire at IOC storage depots since 2009. On October 29, 2009, a fire broke out at its Jaipur terminal which was blamed on non-observance of normal safety procedures.
The Jaipur depot fire raged for 11 days, killed 11 people and resulted in losses worth Rs. 280 crore.
(With inputs from agencies)