whats in a barrel of oil please?, page-10

Costic,
First, you need to specify what gallons
1 US gallon = 0.833 British Imperial gallon;
1 British Imperial gallon = 1.201 US gallons.

1 barrel is 42 US gallons or approx 35 imperial gallons

Also...
- we see that 1 barrel of oil is 158.9873 litre
or approx 159 litres.