You keep saying this. Please link three sources here saying that we can not provide enough crops to support it. Then I can intelligently debate it with you. I don't claim to be an expert and have done very little research myself. But I don't just buy it because someone said so.
OK.
This article references some production figures for how many gallons of ethanol per acre can be produced at various ethanol plants. The best figure is 464 gallons per acre, but for simplicity of calculations, we'll optimistically assume a production level of 500 gallons of ethanol per acre.
This article indicates US gasoline consumption at 146 billion gallons annually.
This article indicates that it takes 1.4 gallons of ethanol to equal the output of 1 gallon of gasoline.
So it's simple math. If we use 146 billion gallons of gasoline per year, then multiplying by 1.4 brings that figure to 204.4 billion gallons of ethanol to displace gasoline. Optimistically assuming 500 gallons of ethanol per acre, that means we'd need 408.8 million acres of corn dedicated to ethanol production to produce the required 204.4 billion gallons of ethanol.
And according to
this article farmers have planted an enormous amount of corn this year: 75.6 million acres, a figure which is expected to increase from what I can tell to around 89 million acres.
Nevertheless, 85 million acres is far short of the optimistic 408.8 million acres. And we're talking about displacing gasoline; we haven't even begun talking about displacing fuels used for heavy industry like diesel and jet fuel and heating oil. And let's not forget that people actually need to eat to, ya know. We're also not figuring in the fuels used to create the ethanol in the first place.
Ethanol is a bad idea. You can mix it with gasoline if you want, but you don't get good benefit from ethanol unless you run it in a high compression engine. And an engine of sufficiently high compression is to high for even 93 octane gasoline; you'd get severe knocking in the engine. Flex fuel vehicles can't get much energy from ethanol because they have to run at low enough compression suitable for gasoline.
You'd need to get 5 times as much ethanol as we presently can from an acre of corn, 2500 gallons, just to keep our gasoline power cars running (again not dealing with diesel yet), and that's assuming we can do without eating corn.
This whole idea is a complete non-starter. Our arable land is not up to this. Look elsewhere for a fuel source.