Nine people were initially said to have died and more than 50 vehicles were burned when a truck carrying 33,000 liters (8,700 US gallons) of petrol suffered brake failure and crashed last Thursday.
But the sheer size of the blaze and the fact that it occurred on a gridlocked road at rush hour have spurred fears that the toll could be higher.
Lagos state health commissioner Jide Idris told reporters on Monday the “completely burnt” bodies of 10 people, including a minor, were recovered from the scene.
Two others later died of severe burns in the hospital.
“The government (will) be conducting DNA forensic studies so that the right bodies can be handed over to the appropriate families for burial,” he said.
The state government has said it is looking to prosecute the owner of the tanker and driver over the truck’s roadworthiness.
Petrol tanker fires are not uncommon on Nigeria’s roads, which are often in disrepair and where vehicles are frequently old and badly maintained.
Blocks are often put behind the wheels of aging, rusting trucks when they are stationary in traffic.