If I want to, lets say trade oil for copper, then you have to have 2 resources of oil and the other guy has to have two copper, right? Makes it quite hard to trade 
Happened to me last game anyway. I traded some resource whatever it was, and after that it was gone, and my GF I played with (at home in LAN) made the same mistake, she lost what she traded with me cause she also only had one resource. No warnings though, and they all show up in available trades.
Manual is pretty sparse (or maybe you have to really dig deep and read between the lines hehe), but I'd like to know what happens if you want to trade a resource with two others. Do you have to have 3 sources of it then to be able to also keep it for yourself or? Anybody know this?
I think that in Civ 3 resources didn't appear to trade if you only had one, so you couldn't trade something away and loose it yourself.

Happened to me last game anyway. I traded some resource whatever it was, and after that it was gone, and my GF I played with (at home in LAN) made the same mistake, she lost what she traded with me cause she also only had one resource. No warnings though, and they all show up in available trades.
Manual is pretty sparse (or maybe you have to really dig deep and read between the lines hehe), but I'd like to know what happens if you want to trade a resource with two others. Do you have to have 3 sources of it then to be able to also keep it for yourself or? Anybody know this?
I think that in Civ 3 resources didn't appear to trade if you only had one, so you couldn't trade something away and loose it yourself.