true, it is indeed hard to tell on some machines, my weedwacker, chainsaw, antique outboard, lawnboy, not so much, kinda a waste of money but i run one mix for every two stroke i got and even one 4 stroke. when i got sick of the price of good oil i switch to quicksilver which is a great oil and didn;t notice much difference. then i down graded to the cheap motomaster outboard crap. after a few tanks....my ski wasn't running as pissed off feeling as it should, my 2008 stock banshee needed 10 kicks to start instead of 1 kick. I switched back to full synth. changed my plugs and all is good again. so yeah which oil is best? who knows, i use amsoil. for me the more important part is that it is a really good oil which will give good lube, clean the internals, protect against moisture, and actually burn with the fuel instead of slugging it down. i was told by a techy geek that gp bike racers gained 3mph when the switched to a high quality synth. just my thoughts on oil.