Nothing, just run your engine like you always do. The non oxygenated fuel is better then the oxygenated engine in away, since there at a higher octain rating then oxygenated fuel. Take note that the higher octane rated fuel has a longer burn rate and will casue carbon build up to low compression engine's due to unburnt fuel. That is why when your car is recomened octain fuel 87%, filling up with a higher octane rating will casue more damage then the low octane rating which is the most confusing part to the public. A higher compression ratio engine needs a higher octane rated fuel to keep the engine from knocking (Detonation) such as the Camaro's and Mustang's.
With that said, the oxygenated fuels has the potental separation (varnish) and corrosion issues, that sit in the gas tank for long periods of time.
Long start short, you may feel a bit more HP and better gas mileage from your Envoy. But you may also get a Service engine light too, the Oxigenated gas was made for emission reasions and run about 1-3 mpg less then the non-oxygenated gas.
Hope i made some sence, it's late and i just drove the tour bus 500 miles today.
