In my 1.9L DOHC 2002 Saturn SC2 with 53,000 plus miles:
Before using Ethos Fuel Re-formulator - 25 mpg to 25.75 mpg
After first Ethos Fuel Re-formulator treatment - 27.70 mpg
After second Ethos Fuel Re-formulator treatment - 32.63 mpg
After third Ethos Fuel Re-formulator treatment - 34.93 mpg
All driving was on my daily commute (25% highway, 75% city streets
Note: The larger your engine, the bigger your savings will be.