If you take into account the value of your personal labor to do an oil change, which I figure is $15.00-$20.00, you don't have to run super long drain intervals to make Amsoil cost effective. The majority of my professional customers w/ high end vehicles don't change their own oil, but have it done at a Quick Lube or new car dealership. These are realistic numbers for that comparison....
For 15,000 miles of driving:
Five petroleum oil changes @ $25.00/change, for a total of $125.00.
Two Amsoil synthetic oil changes @ $60.00; including five quarts of synthetic @ $6.50/qt retail, $12.00 for the Amsoil "Super Duty" oil filter and $15.00 labor.
So you can see, that even with a very conservative, 7500 mile/12,000km, Amsoil change interval, the cost of materials and labor is a wash - not counting any potential fuel savings. With the Amsoil option you have the convenience of eliminating three out of every five oil/filter changes; you reduce the # of waste materials you generate and you get better engine protection and a small increase in performance. You still bring the car in about twice a year, so that the fluid levels, air filter, etc can be checked and somebody has the chance to peek under the car to detect potential problems. For the 60%-70% of vehicle owners who DON'T change their own oil, it's a no-brainer ...
As a final note, if you work through the numbers for the ultra premium, Amsoil Series 2000/3000, you find the break even point is only 10,000 miles/16,000 km. That's the other option I recommend for folks who want to use the absolute best oil I have available ...
TS