【How-to】How much ethanol is in 91 octane gas

According to Dan McTeague, a noted petroleum analyst, Shell and Esso 91 are both ethanol free. … The octane rating of pure ethanol is 100, but when it’s blended with gasoline, it performs as if it’s 112. In other words, higher-octane blends — Petro Canada’s 94 and Esso’s 93 — use more ethanol, not less.