On Wednesday, one floor trader bought 1,000 barrels, the smallest amount permitted, and sold it immediately for $99.40 at a $600 loss, said Stephen Schork, a former floor trader on the New York Mercantile Exchange and the editor of an oil market newsletter.
"They absolutely overpaid," he told Radio Four's Today Programme.
"He paid $600 for the right to tell his grandchildren that he was the first in the world to buy $100 oil."
Most trading in energy futures has shifted away from the trading floor and takes place on electronic platforms.
-Single trader behind oil record