Which oilfield of India has the largest quantity of recoverable petroleum reserves among the following options?

Introduction / Context:
India's crude oil production depends on several major oilfields, both onshore and offshore. Mumbai High, located in the Arabian Sea off the coast of Maharashtra, is one of the most important offshore fields. Exam questions often ask which field has the largest recoverable reserves, as this highlights the economic importance of particular regions in the national energy scenario.

Given Data / Assumptions:
• Four oilfields are listed: Moran, Mumbai High, Ankleshwar and Naharkatiya. • The question asks which of these has the largest recoverable reserves of petroleum. • We focus on long term average assessments of reserves, not short term production fluctuations.

Concept / Approach:
Mumbai High is an offshore oilfield discovered in the 1970s and has long been the largest contributor to India's crude oil output. It has substantial recoverable reserves compared to the older onshore fields of Assam such as Moran and Naharkatiya or the Ankleshwar field in Gujarat. Therefore, when the question asks about the largest recoverable reserves among the listed options, Mumbai High is the correct choice.

Step-by-Step Solution:
Step 1: Recall that Mumbai High is an offshore field in the Arabian Sea, operated by India's national oil company, and is widely recognised as a major source of crude oil. Step 2: Note that Moran, Ankleshwar and Naharkatiya are important onshore fields but are smaller in terms of total reserves compared to Mumbai High. Step 3: Understand that the phrase largest quantity of recoverable reserves refers to how much oil can be economically extracted over the lifetime of the field, not just present production rates. Step 4: Based on these comparisons, select Mumbai High oilfield as the correct answer.

Verification / Alternative check:
Energy sector reports and geography textbooks consistently describe Mumbai High as India's largest offshore oilfield with the biggest share of the country's recoverable crude reserves among the fields listed. Although Assam and Gujarat fields were discovered earlier, they have more limited reserves compared to this offshore giant.

Why Other Options Are Wrong:
Option A (Moran oilfield) is an onshore field in Assam, important but significantly smaller than Mumbai High in total reserves. Option C (Ankleshwar oilfield) in Gujarat is a major onshore oil and gas field, yet its recoverable reserves are much less than those of Mumbai High. Option D (Naharkatiya oilfield) is another Assamese field with notable production but not the largest in India.

Common Pitfalls:
• Learners familiar with the historical significance of Assam's oilfields sometimes overestimate their size relative to modern offshore fields. • Others may mix up the concept of earliest discovered field with largest reserves, which are two different facts.

Final Answer:
Among the listed oilfields, the one with the largest recoverable reserves is Mumbai High oilfield.