If you think of getting a job in IOCL then you must have to clear GATE exam in that respective year.
However, you have to clear IOCL GATE Cut off marks for GD/GT/Interview for mechanical engineering is GEN(80Marks) OBC(75Marks) SC(65Marks) ST(60Marks) with respect to last year data.

Here is the link to PSU recruitment throughGATE2018:-https://engineering.careers360.com/articles/psu-recruitment-through-gate

And if you think of getting a job in Indian Railway then you have to clear IES exam in that respective year. IES exam pattern of two stages; stage:1 is IES Prelims and stage:2 is IES Mains.Here are the list of different IES post for ME.

• Indian Railway Service of Mechanical Engineers
• Central Power Engineering Service
• Indian Naval Armament Service
• Central Engineering Service (Roads) Indian Navy
• Geological Survey of India
• Indian Supply Service
• Central Electrical & Mechanical Engineering Service
• Electrical and Mechanical Engineers, a branch in the Indian Army
• Indian Defence Service of Engineers