The results of fuel-price ratios imply that in the US, where the average price of gasoline hovers at around $3/gallon, the sale price of alternative fuel at the pump needs to be no more than $1.50–1.80/gge (gallon gasoline equivalent) in order to achieve widespread acceptance among general consumers. For E85, which has a reported net 5–15% drop in fuel economy for most flex-fuel vehicles not optimized for it, the retail price needs to be even lower, in the range of $1.30–1.70/gge. Alternatively, federal and state subsidies to lower AFV investment/conversion costs would need to be large enough to decrease the payback period to below 3 years. Other government-provided financial and non-financial incentives offered to a wide range of stakeholders, as well as regulations and programs to promote information sharing and industry coalitions, will play important roles in promoting the penetration of AFVs. The extents to which these factors affect penetration, and the mechanisms by which they do so, require further study.