Yes, you can apply RTI to Indian Oil Corporation Limited (IOCL).
IOCL commonly known as IndianOil is an Indian State owned Oil and Gas Company with registered office at Mumbai and primarily headquartered in New Delhi. IOCL was established as an Oil Marketing Entity on 30th June 1959, Indian Oil Company Ltd. was renamed Indian Oil Corporation Ltd. on 1st September 1964 following the merger of Indian Refineries Ltd. (established in August 1958). As of September 2018, it was owned 57% by the Government of India (through the President of India), and 43% by other entities.
IOCL is a "Public Authority" as per Section 2 (h) of the RTI Act.
You can file RTI to IOCL by paying the prescribed fee either Online or through Offline mode.
To know more about the procedure to file RTI Applications Online for Central Govt. Departments, please refer https://onlinerti.com/how-to-file-rti-online-for-center