Hey as Oil and Natural Gas Corporation Limited is an Indian multinational oil and gas company headquartered in Dehradun, Uttarakhand, India

Here I am giving you some books for ONGC exam
General English For ONGC Exams Prep Course by GK Publishers
Study Guide to General Engineering for ONGC and other Public Sector Examinations
ONGC Civil Asst Executive Engineering Recruitment Examination
ONGC - Officer Recruitment Examination - Finance & Accounts English 2015 Edition
ONGC Mechanical Assistant Executive Engineer Recruitment Examination English 1st Edition
ONGC Instrumentation Asst. Executive Engineering Recruitment Examination

Nationality
Candidate should be Indian

Qualification required
Candidate should be graduate from recognised university

Exam pattern
Aptitude ( Around 50 question)
General Awareness ( Around 50 question)
Subject Knowledge ( Around 100 question)
Aptitude test section contains Comprehension, Reasoning (Verbal/Non-verbal), Numerical Ability/Quantitative Aptitude, Data Interpretation.

Selection criteria
Written Test .
Personal Interview.
Medical examination.