[Piwoslaw]

I heard a commercial on the radio today where Shell claims it has fuel-saving gasoline and fuel-saving diesel. So this raised two questions:

1. Can a fuel help reduce consumption? And I don't mean changing the octane number to fiddle with compression and timing, just filling up with the new fuel and driving off, happy that I'm consuming less. And if it is just better quality, then does this mean that Shell has been giving us lower-grade fuel, yet advertising it as "Highest quality, premium, etc."?
2. How much can it actually increase FE without help from anything else (changing driving style). Is Shell just counting on the placebo effect?
3. Is a 1-3% decrease in fuel consumption worth the 5-10% higher price? (I'm just guessing, I don't know the exact numbers.)