PhD in Petroleum Engineering: Is it worth it?

[virtua]

I`m an international male student (non-US citizen), who have been accepted to PhD at the university, which is in ranking not top, but not at the bottom either. I have been offered Research Assistantship. I don`t think that salary is high, but I hope it is enough to live in the city where the university is located, but I don`t think that I will be able to save up some money with that salary.

And I have to answer to this offer till some approaching deadline, but I still haven`t received answers from the other universities to which I applied for MSc (well, actually, I have received answers from 2 of them: I have been accepted, but they dont offer me any assistantship).

There are many questions in my head, but in summary, I would like to ask for advice, what do you think, guys, is it worth to spend 4-5 years doing PhD in an average university (but with very good lab)? Is there anything that I will gain after it?

I would like you, guys, to share your experience; has anyone who did PhD felt that it made a difference in his/her life?

Thanks in advance.