Hey!

There is nothing such 'best' specialization in this stream. As companies accept wide range of variety as specialists and engineers need to be flexible to stay with the change in oil and gas sector. There are some most popular specializations in this area are drilling engineering, production engineering, Reservoir engineering, petrophysical engineering, etc. It depends on the candidate what job profile he wants like supervision, administration, etc or where he wants to work (onshore, offshore, foreign, etc)  However, petroleum Reservoir has been considered as very flexible specialization of this field.

Hope it helped to clear your delimma

Thank you