hello sir, i'm interested in doing petroleum engineering. my question is can i do mechanical engineering and then go for masters in petroleum enigineering?

Yes, it's definitely possible. You may also want to think of doing an MBA in Oil and Gas management at UPES with distance learning. Graduation with minimum 50% marks in any discipline (preferably with science, technology and commerce background) with minimum two years (2) of experience in oil or gas

Yes you can pursue a bachelors in mechanical engineering and then target masters in petroleum engineering. Even though the masters requirement would recommend you to have a bachelors in petroleum engineering, they would also accept degrees from different backgrounds.