Jeffery,

I think you missed Memmel's point. Think of it like an energy balance a ChemE would use when designing a plant. I believe his thrust was that although Mex exports oil to the US, the US exports "oil equivalents" via grain to Mex. Therefore, it isn't a simple one way street and that these "equivalents" have to included in the calculation.

Todd

I'd only count the portion that actually gets used as fuel (and not as human or animal feed). Otherwise you're on the slippery slope of saying that you have to include X as it is a product of the import and it is exported to Mexico.

Of course, getting those stats could be a bit tricky.

Why does it matter what goes back? What keeps the system going is the input...and that is barrels of oil. Everything else is derived from that.

It's like having two mirrors facing each other. Sure, the reflections and counter-reflections go on forever but take away one mirror and everything stops.