If it's oiled wire, stored in oiled paper, it's actually meant for concrete work with re-bar, but is actually used most often to string low-charge electric fences. It is commonly used with horses in conjunction with white, vinyl warning fence. You get anywhere from 50-200 feet per spool.
Baling wire is substantially thicker, un-oiled, and comes in much larger spools; 500-1000 feet per spool.
The spools in oil paper are meant to be strung by hand and not intended to be used for tying anything long-term; hence the lighter gauge. In fact, it's meant to hold re-bar together long enough for the concrete to be poured, thereby securing the re-bar and negating the need for the wire. Baling wire is intended to be strung by machine, and exists mainly to tie things together for seasons (and hold together the entire Midwest's infrastructure). Square bales that use baling wire must be stored out of the elements, so the wire being un-oiled is not an issue.
To the GP: If you use baling twine, then your machinery sucks, sell that P.O.S. Oliver and buy something made in the last fifty years. I bet you run narrow base Allis-Chalmers too, don't you?