Yes, depending on what rate you blend it at. Ethanol has a lower energy value than petroleum. That's not to be mistaken for energy balance, which is how much energy you get out of it versus how much it takes to produce it; that's positive, at about twice as much energy out. But there's a lower BTU value, so at higher concentration blends--the article was correct in referencing 85% ethanol--you would see about a 25% reduction in gas mileage associated with that.
On September 25th, 2006. See this statement in context.