With a single small deal, an independent trader on Wednesday secured his place in market history by pushing oil prices briefly to the unprecedented level of $100 a barrel.

Some observers questioned the validity of the price mark when it emerged that the peak was the result of a trader – one of the “locals” who trade on their own money – buying from a colleague just 1,000 barrels of crude, the minimum allowed, industry insiders said. The deal on the floor of the New York Mercantile Exchange was at a hefty premium to prevailing prices.