Yes, you can file RTI Applications to Gas Authority of India Limited (GAIL).
Gail (India) Limited (GAIL), formerly known as Gas Authority of India Limited is the largest state-owned natural gas processing and distribution company in India. GAIL was conferred with the Maharatna status on 01/02/2013, by Government of India. GAIL comes under under the Ministry of Petroleum & Natural Gas. GAIL is a Public Authority as per Section 2 (h) of the RTI Act 2005 and comes under the ambit of the Act.
Hence, you can apply RTI to GAIL by paying the prescribe fee either Online or Offline mode.
To know the further procedure for filing RTI's Online please refer, https://onlinerti.com/how-to-file-rti-online-for-center