Are there fuel additives that will increase my gas mileage?

Well, I won't make that an absolute no. It depends on how old your car is. If you own a car that was built in the last 15 years or so, it has <a rel="nofollow" href="http://auto.howstuffworks.com/fuel-injection.htm" target="_blank">programmed fuel injection</a>. A computer monitors a number of sensors located at various points in your intake system, the engine itself, and the exhaust. The computer knows when the engine is cold, and delivers the extra fuel it needs to warm up. When the engine is at operating temperature, it monitors the amount of oxygen in the exhaust gas to adjust the air/fuel ratio to its ideal proportions. This is called the stoichiometric ratio. For a gasoline engine, this is 14.7 parts of air for each part of fuel, by weight, and the computer adjusts fuel delivery to maintain this ratio. No fuel additive will have any real effect on it. The stoichiometric ratio for different types of fuels varies, but when you consider how these things are sold - in 8-oz bottles, ...  more

Well, I won't make that an absolute no. It depends on how old your car is. If you own a car that was built in the last 15 years or so, it has <a rel="nofollow" href="http://auto.howstuffworks.com/fuel-injection.htm" target="_blank">programmed fuel injection</a>. A computer monitors a number of sensors located at various points in your intake system, the engine itself, and the exhaust. The computer knows when the engine is cold, and delivers the extra fuel it needs to warm up. When the engine is at operating temperature, it monitors the amount of oxygen in the exhaust gas to adjust the air/fuel ratio to its ideal proportions. This is called the stoichiometric ratio. For a gasoline engine, this is 14.7 parts of air for each part of fuel, by weight, and the computer adjusts fuel delivery to maintain this ratio. No fuel additive will have any real effect on it. The stoichiometric ratio for different types of fuels varies, but when you consider how these things are sold - in 8-oz bottles, ...  more