AMSOIL Signature Series 0W-30 Synthetic Motor Oil is recommended for extended drain intervals in unmodified(1), mechanically sound(2) gasoline fueled vehicles as follows:
• Normal Service(3) – Up to 35,000 miles or one year, whichever comes first.
• Severe Service(4) – Up to 17,500 miles or one year, whichever comes first.
• Replace AMSOIL Ea oil filter at the time of oil change up to 25,000 miles or one year, whichever comes first (other brands at standard OEM* intervals).
• In all non-gasoline fueled vehicle applications, extend the oil change interval according to oil analysis or follow the OEM* drain interval.
Seems your numbers are off a bit but this is a quality product and to me there is no such animal as Normal Service and why people think there is I have no clue? This is the info on the 11.00 per Qt Amsoil and Severe Service which i classify just about every vehicle says 17.5K or 1 Year which ever comes first. The 7.00 dollar Amsoil Oil products are supposed to be changed sooner per their website and also have a 1 year change requirement. I concur this type of oil will increase your MPG but your theory of cheaper ways to achieve this have gone astray rather quickly given the price of Amsoil, cheapest at about 7 bucks a Qt or 50 bucks before shipping and tax?