Castrol GP MC oil is SG rated. The SG rated oils are high in ZDDP additive (Zinc dialkyldithiophosphates) Look it up if you don't know what it is. SG rated oils came out in 1988. This API rating has been superseded many times over by now. An SG rated oil is particularly good for older air or oil cooled engines. ZDDP is important for engines that have flat tappet cam followers. All of you know what those are, right? API rated oils like SL or SN have lower ZDDP content. This additive is supposed to be bad for catalytic converters, and that is one reason it has been reduced in newer oils. (That high ZDDP content is probably why SG rated oil is still available today) GP is 100% Dino oil. My BMW 2002, r1150rs requires the 20W-50 version, and that is all I have ever used. The bike has over 220000km, and she runs perfect. The engine has never required any service or repairs, just new spark plugs and valve clearance adjustments. I follow the manufacturers oil change interval which is every 10000km.