Mr Philip Tan, 45, clocks up to 400km a day, ferrying passengers who book rides via the Grab app.
That is more than double what a single-shift taxi will register on average, as well as nine times the mileage of an average family car.
Private-hire car drivers such as Mr Tan are a likely reason why Singapore's petrol consumption is on the rise despite the vehicle population shrinking, say experts.
The Republic is set to consume a record 6,453,600 barrels of petrol this year, 5.6 per cent more than in 2013.
Before he switched to a diesel Kia Carens in September, Mr Tan estimated he was spending $80 a day, after discount, for about 40 litres of petrol for his Honda Stream.
He does between 30 and 35 trips a day, and said he made the change for economic reasons.
"For the Kia, $55 will get me a full tank, which can go up to 1,000km. I have to top up the tank only every two to three days," he said.
The bulk of private-hire cars, however, are petrol models.
Mr Lim Kong Hong, 48, clocks between 250km and 300km a day in his petrol-engine Honda Stream.
While business on the Grab app has slowed down at the year end - which Mr Lim reckons is due to people being on vacation - bookings typically come in "fast and furious" on the app.
"As one job ends, the next moment you will get another one," he said.
The entry of Uber and Grab in 2013 has doubled the market for point-to-point transportation, the authorities have said, suggesting that there is new or previously unmet demand for taxi or taxi-like services being catered to.
Drivers said commuters are choosing to take private-hire cars for very short trips, or even as an alternative to buses, due to the generous discounts given by Uber and Grab.
Nanyang Technological University undergraduate David Tan, 23, said he uses Grab to travel from his hall residence to his lecture theatres - a five-to seven-minute drive away.
With the $5 discounts on Grab, he does not pay a cent for the fare.
"Grab is more convenient and takes me from my doorstep right up to the lecture theatre.
"The campus shuttle can be crowded, and the waiting times can be long. I know a few friends who also take Grab around the campus," he said.
"If there are no more promotions, I will go back to taking the shuttle bus," he added.