Dear Piyush, the official brouchure states that the relevant link to apply for IOCL through GATE will be open from January 4th on the Indian Oil's official website www.iocl.com. It also suggests to click on ONLINE to fill in the application. However, it is also been said that the applications will be available to be downloaded once the GATE admit card is available to be downloaded. This is because candidates need to enter their GATE registration number on the application. And the application forms haven't been released yet. At this point in time, the only option is to keep an eye on the official website. 

Hello aspirant
I can help you with better information.
Use the below link for  information about the iocl recruitment and application opening date and closing dates.
Link:https://engineering.careers360.com/articles/iocl-recruitment-through-gate
Hope above information is helpful to you
All the best
Thank you