but I'm changing to Castrol R2 as I like the smell better 
but its £13 a litre + £4 p&p
,If your in this country then someone on e bay sells Comp 2 plus in 4 litre cans for £31 inc p&p,I use to buy from them .My 18 does use a lot but I only have another 18 to compare it to but as for its fuel useage,I put 9 litres in yesterday and have done 40 miles and its now back on reserve and I'm only riding it to work and back at a slow-ish speed 
and its stock but this means Iv'e found a use for my R6 as I will be using it for work now as it's cheaper to run that my NSR .