Average oil consumption for heating?

mods, feel free to move if in the wron forum...

My colleague asked me to ask you
He moved to a detached bungalow with 3 bedrooms and and has bought not even 2 month ago his first oil to fill up the tank. He said he bough 500 liters and yesterday he noticed that the heater is not working anymore so he went and checked the oil tank - and it was empty.
So basically he used 500 liters in 50 days on a average heating time of 5 hours daily for one bedroom, kitchen, hall, bathroom and living room. Hot water is going via an electrical heated tank.

Is this a normal consumption as it would make 2 litres oil per hour for heating?! or did he got screwed by the oil deliverer and only got 300l instead of 500? You sometimes hear that their meters are not working correctly. The rumour has it...

EDIT/NB: Colleague said there is no leak.

thanks for any advise
talking clock