U.S. securities regulators were probing unusual activity in Airgas call options before a $5.1 billion offer for the industrial gas company was announced, a person familiar with the probe said on Wednesday.

Air Products launched an unsolicited $60-a-share cash bid for rival Airgas Feb. 5, prompting AirGas'shares to jump. The Securities and Exchange Commission is looking into potential insider trading in Airgas, the person said. The source requested anonymity because the probe has not been made public.