£18 seems quite expensive.
Why does engine oil cost more per litre than diesel, when diesel price is mostly tax?
There was a letter in Diesel Car magazine, Feb 2005, issue 203. (www.dieselcar.com)
" Myself and two other motoring enthusiasts got together to find a cheaper way of getting quality oil at a better price. We each agreed to accept a 20 litre container and, armed with an order for our 60 litres. I went to a local oil distributor to get a price for some fully synthetic oil in this case Total Quartz 9000 5w/40. In January 2004 I was quoted £1.45 per litre including vat. When we eventually went to order in October we had expected a price rise – what with the escalating cost of crude oil. We were then quoted £1.20 per litre, plus vat and I could barely believe it! I was told that it was because the order was placed at the beginning of the month! That worked out at £7.05 for 5 litres, delivered to my front door. Apparently we were classed as "bulk-buyers"."