Actually they had *different* vents. The vent came out the nozzle next to the gasoline. From what I read it was to prevent over filling fuel tanks. When the fuel reached the vent it would block it so no more air could go into the can, and supposedly that would stop any more fuel from coming out. Right, a plastic gas can without a vent? The sides bend in and fuel still comes out. Then it gurgles and spits out another cup or so on the mower and/or ground. I really wish I knew what moron approved that style container.
They did stop making that type. I'm not sure what is mandatory now (for new containers).