Neither, it inhibits the absorption of water but does not remove the oxygen content.
Q: What is the difference between STA-BIl Fuel Stabilizer, Marine Formula STA-BIL, and the new STA-BIL Ethanol Treatment products?
A: STA-BIL® Fuel Stabilizer is designed for use during STORAGE of any gasoline equipment or vehicle stored for 30 days or more, or used infrequently. It will keep gas fresh for 12 months, and help prevent corrosion, and gum and varnish formation. It is effective in all gasolines, including Ethanol blends, including E-85.
Marine Formula STA-BIL® Ethanol Treatment was designed for use at every fill up for marine engines (boats, jetskis) to protect against the damaging effects experienced when using Ethanol blended fuels -- including corrosion caused by water attraction, and fuel system plugging caused by deposit loosening.
New STA-BIL Ethanol Treatment is designed for use at every fill up for all gasoline automotive and small engines for protection against these same problems.
See my post #22. I much prefer the Amzoil product; it saved 3 small engines for me. I do drain the gas out of each at the end of the season though.