I don't know about the nuts and bolts of which is more energy efficient per ton, but would bet on ships over aircraft any day. You also have to look at cargo space utilization. Look at the history of transportation, as cheap energy was discovered and utilized "time" became the measured efficiency factor, I think as fuel cost rise time will become less of a factor. We used to move freight by stage coach and wagon, then the trains. I have a book that has the history of one branch of my family. One of the sons left NY to head for the West Coast. He took a bunch of farming and mining equipment with him on the ship, it took almost 300 days to get there. Once he sold the initial stock, he reordered and had half sent by wagon train, half by ship. At one point he was having stuff sent by rail but was complaining about the exorbitant costs It will boil down to how soon vs how much do you want to pay. We deal with that quite regularly in my wife's bridal shop. The ladies want a particular dress, but have waited until the last minute. Not too many people are willing to double the cost of a dress for a Super Rush Cut and quite often will chose something that is either available from store stock or on a shorter lead time. Our company tracks the cost of all items we have shipped, we actually have different accounting codes to indicate how much we spend on overnight vs ground vs LTL and dedicated full trucks. We have been instructed to utilize overnight as a last resort. In the words of our CFO "poor prior planning does not mean airfreight is the only solution"

Aaron