Not an accountant nor a lawyer neither.

But not against saving a couple of thousand dollars a year
e.g. 60000km @ 6km/litre = 10,000 litres of fuel used and 60000 @ 7km/litre = 8571 litres of fuel used - 10000 - 8571 = 1429 : 1429 litres x $1.50 = $2143.50 savings on fuel cost p.a.

Worth having in my pocket I reckon.