Sugar #11 is sometimes called "international sugar", Sugar #14 is called "domestic sugar", and Sugar #5 is refined beet sugar (aka "white").
Sugar #14 specifically calls for sugar delivered at ports in the US.
Sugar #11 is freely traded, sugar #14 is subject to a wide variety of American trade restrictions, price support structures, etc.
Before jumping into the spread, you'd have to understand what the governmental maneuvering is to know why there's a spread between #11 and #14.
#11 versus #5 might be an interesting spread (the latter trading at LIFFE), both are free from US trade controls.
