A team of Pennzoil marketing guys stopped by work the other day to enlighten us lowly peons to Shell's range of magical wonder juice. Some select points they made... If a 0W-xx is available in the hot-temp grade you need, there's no reason to use a 5W-xx or 10W-xx (or, God forbid, a 15W-xx). They are all equally shear stable over the life of the oil. Conventional oils have a service life exactly the same as any synthetic, in all applications. Synthetic oil will increase your fuel economy by an average of 4.1% over conventional. Not talking a clean vs. dirty engine...just by switching to synthetic. All oil, synthetic or conventional, comes from crude oil (unless it's GTL, of course). PAOs/esters too. Synthetic oils are the best choice for any vehicle. Extremely high mileage ones with leaks too. This one really tickled me because they mentioned it right after saying synthetics won't cause leaks, but will uncover them. (Hey everyone, let's find a problem and make it worse!) I can't necessarily speak for the validity of the 'they all come from crude' remark, but the rest made me wince. At least they bought lunch.