The whistleblower, named as Seth Freedman, claimed the gas market has been "regularly" manipulated by some of the big power companies, the Guardian reports.
Mr Freedman, who works as a price reporter for ICIS Heren, a company responsible for setting so-called benchmark prices, raised the alarm after identifying what he believed to be attempts to distort the prices reported by the company.
It was also reported that Ofgem has been warned by ICIS Heren that it has seen evidence of suspect trading on September 28, the date that marks the end of the gas financial year.
A Department of Energy and Climate Change spokesman said the Government takes alleged abuse in markets "very seriously".
A former energy trader has told ITV News the electricity market has been rigged and it is "worse" than the gas market.
Another market, another investigation. The Energy and City watchdogs start investigations into allegations of traders fixing the gas price.