I have the Barclays World MC and I may soon be making a large cash purchase (a car). So I figure that I might as well use my CC and get the miles.

But the item will cost more than my credit line. Yet when I called Barclays, I was told that because I have a "World Card", I can go over my credit limit without penalty. "OK," I said, "that's nice to know -- but how much can I go over my credit limit?"

"You have no preset spending limit," the agent repeated.

"There must be a limit," I said.

"No, sir."

"But surely," I said, "I could not go and buy a $10,000,000 yacht with my card."

"You have no preset spending limit," the automaton -- err, the agent -- repeated.

OK, so what's the real deal? How far over your credit line can you go with the USAir Barclays World MC?