A $1.8 billion futures trade that fuelled buying in the US stock market on December 7 was the biggest transaction of its kind all year, according to new analysis, and comparable in size to the “fat finger” trade said to have set off the May 2010 “flash crash.”

The analysis by MayStreet, a market data firm, shows that an unknown buyer on Dec. 7 purchased around 16,000 E-mini S&P 500 futures contracts at 1:21 p.m. New York time.