10w-40 will generally be a semi synthetic and is the basic recomendation. 0w-40 and 5w-40 are synthetics and think of them as an upgrade in performance and quality. The Castrol has changed name and it is now called the Castrol Edge Sport 0w-40 here http://www.opieoils.co.uk/p-718-cast...n-engines.aspx

Cheers

Guy