Reservoir Engineers quantify how much oil and gas sits in a subsurface formation, how fast it can be extracted, and what interventions — waterflooding, gas injection, polymer flooding, infill drilling — will maximise total recovery before abandonment. In India the role concentrates at ONGC (Western Offshore Mumbai High, KG Basin, Rajasthan Barmer, Cambay, Assam), Oil India (Assam, Rajasthan), Cairn Oil & Gas / Vedanta (Barmer Mangala / Bhagyam / Shakti cluster), Reliance E&P (KG-D6 deepwater), and the oilfield services technology companies (Schlumberger / SLB, Halliburton, Baker Hughes) that provide reservoir-simulation and integrated-asset modelling services across all these assets. Day-to-day work spans reservoir-model building and history-matching in Eclipse or CMG (IMEX, STARS, GEM), decline-curve analysis (Arps / multi-segment) in OFM / Spotfire, material-balance modelling in MBAL, well-test interpretation and pressure-transient analysis in KAPPA Saphir / PanSystem, probabilistic volumetric estimation at P10/P50/P90, integrated field-development planning, and IOR/EOR study design for ageing fields. The primary feeder is B.Tech or M.Tech in Petroleum Engineering from IIT-ISM Dhanbad, PDEU/PDEU Gandhinagar, RGIPT Jais, or UPES Dehradun; ONGC and OIL hire via GATE (Petroleum Engineering) and their own written exams; private E&P and OFS hire through campus at IIT-ISM and lateral transfers.