Nine investment banks are selling $136m (€103m) of shares in the New York Mercantile Exchange after the value of their holdings in the US commodities market doubled since it went public three months ago.

Nymex has filed with the Securities and Exchange Commission, the US regulator, for a secondary offering. Merrill Lynch and JP Morgan, which led the initial public offering, are selling $31m and $8m Nymex shares respectively and will each retain a $39m stake, according to the filing.