It would be difficult to land a job in petroleum engineering with just an mba… Obviously it sounds like you want to do a specialized course in petroleum & work your way up. In other words, you will have to start from scratch in order to shift gear from MBA to Petroleum. There is no short cut here. Try to earn a bachelors in petroleum or any other relevant engineering field. Afterwards you can work to get a certificate… Visit http://spe.org/training/certification.php
I currently have an MBA but would like to earn a degree that qualifies me for work in the petroleum industry. Is there a specific degree that would complement my current education without having to start over from scratch?