Brent traders

Can anyone familiar with the north sea crude physical market help me understand how the whole "wet barrel" thing works?

I've read that there's a time period in which a bunch of traders just buy and sell paper back and forth to each other in a rapid fire mode until the final guy gets the hot potato. Something like that. But can't find much info on why this happens (why are you forced to buy from some other guy?) and what's the point of participating in this  market.