I can relate, I was in a similar situation when I started preparing for the GATE exam. I had a strong foundation but felt a bit lost on how to land jobs in PSUs. While internships at oil and gas companies, such as ONGC and IOCL, can be beneficial, they aren't absolutely necessary. Your GATE score is what's really important. If you have the chance to work on a project or undergo training with these companies, that's fantastic, it really helps build confidence and demonstrates your initiative. But if that's not possible, don't stress too much. Just concentrate on your GATE prep and look for any engineering internships that will give you some practical experience.