Hello aspirant, 

Petroleum engineering has three streams : Upstream, gas and downstream. Well, it is a stream in which you work on Petroleum, getting the crude oil to refining it, to sell it to customers. There are many companies who hire Petroleum engineers like Schlumberger, Halliburton, cairn oil and gas, she'll, baker Hughes, L&T and many more. Also for government jobs: ongc, hp, indian oil etc. 

Hope it helped to clear your delimma