I saw on the news about a gas additive which improved gas milage and carbon dioxcide release.

Does anyone here have any comments on these type products. How does this affect the engine/transmission for prolonged use?

Right now I am happy with my milage but I think that in the future I will like to try(or need) a product simular to what was presented.

What experience have any of you had using these products. Are they highly recommnded?

Also does anyone know about the octanes available when you purchase gas at the store? Like I get confused about the 3 choices offered and I have heard not to get the highest number-however why is it available if it is a bad thing?