Originally Posted by GZRider
The scale of a dragon, a wolf's tooth, a witch's mummified flesh, the gullet and stomach of a ravenous shark, a root of hemlock that was dug up in the dark, group LXIX base oils, the tears of a virgin unicorn, and a piece of the Golden Fleece. Sorry I'll show myself out now.
...‚.. that's funny.
OP, it's both. Of course a higher pao/ester content is going to allow the finished lube to perform over long(er) drain intervals but you also need additives that aren't going to deplete at 15k miles. Dispersants, VM's, antioxidants and detergents all gotta stay active for a longer period or the lubes in trouble. Of course good filtration plays an equally important part in extended drain intervals.
If you're seeking exact %'s and types (additives), good luck. You're gonna need to contact XOM for that.