Hi Avijet,

The best PSU for an instrumentation engineer in overall aspect is IOCL.

In terms of salary first is ONGC then NTPC then IOCL, GAIL , BPCL lie at same range and then comes HPCL

Dear Avijeet, 

as of my knowledge Indian Oil Coorporation Ltd is best for an instrumentation engineer. It's a dream company for all of them.

in terms of salary ONGC>NTPC>IOCL=BPCL=GAIL>HPCL

but remember for ONGC be mentally prepared for rough and tough work and Offshore 15 days ON/OFF which is considered the hardest part.

Hope you got your answer.

Good luck :)