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National Oilwell Varco Software Engineer Interview Guide

National Oilwell Varco Software Engineer interview guide: reported rounds, questions and how candidates describe the process.

The 60-second brief

A Software Engineer at National Oilwell Varco (NOV) plays a critical role in bridging the gap between heavy industrial machinery and cutting-edge digital intelligence. As a global leader in oilfield equipment, rig technologies, and industrial operations, National Oilwell Varco relies on its software engineering teams to build, deploy, and maintain the complex control systems, data pipelines, and enterprise applications that power global energy infrastructure. Whether you are developing real-time control systems for multi-million dollar drilling rigs or writing data analytics tools to optimize asset performance, your work directly impacts the safety, efficiency, and sustainability of global operations. Unlike traditional technology firms where software exists purely in the cloud, software engineering at National Oilwell Varco is deeply tangible.

This guide is scoped to a Software Engineer candidate at National Oilwell Varco.

Focus areas

  • Behavioral interview skills
  • Communication skills (technical + interview communication)
  • Project experience storytelling

The National Oilwell Varco interview process

National Oilwell Varco candidates report 4 rounds over 3-5 weeks. The stages below are what candidates describe, not a published process.

Initial Screening

A brief phone call with HR or a hiring manager to review your background and discuss career goals.

What to demonstrate

  • A brief phone call with HR or a hiring manager to review your background and discuss career goals
  • Depth in Behavioral interview skills

How to prepare

  • Be able to walk your CV end to end in two minutes, and say why this company specifically.
  • Have your salary expectations, notice period and location constraints ready, and ask for the rest of the loop in writing.

Technical Evaluation

Involves a coding challenge, take-home test, or technical phone interview focusing on OOP, SQL, and system design.

What to demonstrate

  • Involves a coding challenge, take-home test, or technical phone interview focusing on OOP, SQL, and system design
  • Depth in Behavioral interview skills

How to prepare

  • Answer aloud and timed: Explain how you would implement a standard search algorithm and optimize its time complexity.
  • Answer aloud and timed: Walk through a basic string manipulation problem and discuss how you handle edge cases such as null inputs or special characters.

Onsite / Panel Interview

A multi-hour round including behavioral discussions, whiteboard problem-solving, and a panel interview with engineering leads.

What to demonstrate

  • A multi-hour round including behavioral discussions, whiteboard problem-solving, and a panel interview with engineering leads
  • Depth in Behavioral interview skills

How to prepare

  • Answer aloud and timed: Explain the core pillars of Object-Oriented Programming (OOP) and give a real-world example of how you have applied inheritance and polymorphism in a project.
  • Answer aloud and timed: What is the difference between a Web Service and Windows Communication Foundation (WCF)? When would you choose one over the other?

Facility Tour & Wrap-up

Concludes the onsite interview with a tour of the local manufacturing plant or engineering facility.

What to demonstrate

  • Concludes the onsite interview with a tour of the local manufacturing plant or engineering facility
  • Depth in Behavioral interview skills

How to prepare

  • Answer aloud and timed: Describe the Software Development Life Cycle (SDLC) phases and explain your preferred methodology when managing a fast-paced project.
  • Answer aloud and timed: How would you design a software architecture to handle real-time data streaming from multiple hardware sensors on a drilling rig?

Where candidates lose points

Highlight Practical Projects

When discussing your portfolio, focus on projects where you had to solve real-world problems, optimize performance, or integrate with hardware or external APIs.

Show Enthusiasm for the Industry

Take the time to research NOV's recent innovations and product lines. Showing that you understand the scale and importance of their industrial machinery will make a highly positive impression on the hiring managers.

Brush Up on Databases

Do not skip your SQL preparation. Be ready to write queries on a whiteboard, explain optimization strategies, and discuss data normalization.

Be Honest About Your Skills

If you do not know the answer to a technical question, walk the interviewer through your thought process on how you would find the answer. NOV managers value honesty, logical thinking, and coachability over memorized answers.

Questions & practice

Write a program that takes a list of numbers as input and outputs the missing numbers in the sequence (e.g., I

Medium · Coding & Algorithms

Write a program that takes a list of numbers as input and outputs the missing numbers in the sequence (e.g., Input: [1, 2, 5, 7, 9], Output: [3, 4, 6, 8]).

Approach

  1. Restate the input: its shape, its size, and what is guaranteed about it.
  2. Name the brute-force solution and its complexity before improving on it.
  3. Choose the data structure from the access pattern, not from familiarity.
  4. State the target complexity and say which constraint rules the naive version out.

Follow-up

  • How does this change if the input no longer fits in memory?
  • What is the worst case, and how likely is it on real data?

Analyze a provided code snippet and determine the final value of a specific variable after execution.

Medium · Coding & Algorithms

Approach

  1. Restate the input: its shape, its size, and what is guaranteed about it.
  2. Name the brute-force solution and its complexity before improving on it.
  3. Choose the data structure from the access pattern, not from familiarity.
  4. State the target complexity and say which constraint rules the naive version out.

Follow-up

  • How does this change if the input no longer fits in memory?
  • What is the worst case, and how likely is it on real data?

Explain how you would implement a standard search algorithm and optimize its time complexity.

Medium · Coding & Algorithms

Approach

  1. Restate the input: its shape, its size, and what is guaranteed about it.
  2. Name the brute-force solution and its complexity before improving on it.
  3. Choose the data structure from the access pattern, not from familiarity.
  4. State the target complexity and say which constraint rules the naive version out.

Follow-up

  • How does this change if the input no longer fits in memory?
  • What is the worst case, and how likely is it on real data?

Walk through a basic string manipulation problem and discuss how you handle edge cases such as null inputs or

Medium · Coding & Algorithms

Walk through a basic string manipulation problem and discuss how you handle edge cases such as null inputs or special characters.

Approach

  1. Restate the input: its shape, its size, and what is guaranteed about it.
  2. Name the brute-force solution and its complexity before improving on it.
  3. Choose the data structure from the access pattern, not from familiarity.
  4. State the target complexity and say which constraint rules the naive version out.

Follow-up

  • How does this change if the input no longer fits in memory?
  • What is the worst case, and how likely is it on real data?

Write a SQL Union Query to combine data from three tables sharing the same unique ID.

Medium · Database & SQL

Approach

  1. Name the grain you start from and join outward from it.
  2. Check whether any join is one-to-many before aggregating, or the sums inflate.
  3. Say which index the query would use, and what makes it unusable.
  4. Handle the rows that do not match: that is usually the actual question.

Follow-up

  • How does the query change if that join becomes one-to-many?
  • What happens to this when the table is ten times larger?

What is the difference between DROP, DELETE, and TRUNCATE tables in SQL? Explain the performance and tra

Medium · Database & SQL

What is the difference between DROP, DELETE, and TRUNCATE tables in SQL? Explain the performance and transactional implications of each.

Approach

  1. Name the grain you start from and join outward from it.
  2. Check whether any join is one-to-many before aggregating, or the sums inflate.
  3. Say which index the query would use, and what makes it unusable.
  4. Handle the rows that do not match: that is usually the actual question.

Follow-up

  • How does the query change if that join becomes one-to-many?
  • What happens to this when the table is ten times larger?

How do you design database schemas to ensure data integrity when dealing with relational databases?

Medium · Database & SQL

Approach

  1. Name the grain you start from and join outward from it.
  2. Check whether any join is one-to-many before aggregating, or the sums inflate.
  3. Say which index the query would use, and what makes it unusable.
  4. Handle the rows that do not match: that is usually the actual question.

Follow-up

  • How does the query change if that join becomes one-to-many?
  • What happens to this when the table is ten times larger?

Explain the core pillars of Object-Oriented Programming (OOP) and give a real-world example of how you have ap

Medium · System Design & Object-Oriented Programm

Explain the core pillars of Object-Oriented Programming (OOP) and give a real-world example of how you have applied inheritance and polymorphism in a project.

Approach

  1. Fix the scope first: who calls this, how often, and what they do when it fails.
  2. Name the read and write paths separately; they rarely have the same bottleneck.
  3. Choose a partition key and say what query it makes expensive.
  4. State the consistency you need, and where you are willing to be stale.

Follow-up

  • What breaks first when traffic grows ten times?
  • How does this behave when that dependency is down for an hour?

What is the difference between a Web Service and Windows Communication Foundation (WCF)? When would you choose

Medium · System Design & Object-Oriented Programm

What is the difference between a Web Service and Windows Communication Foundation (WCF)? When would you choose one over the other?

Approach

  1. Fix the scope first: who calls this, how often, and what they do when it fails.
  2. Name the read and write paths separately; they rarely have the same bottleneck.
  3. Choose a partition key and say what query it makes expensive.
  4. State the consistency you need, and where you are willing to be stale.

Follow-up

  • What breaks first when traffic grows ten times?
  • How does this behave when that dependency is down for an hour?

Describe the Software Development Life Cycle (SDLC) phases and explain your preferred methodology when managin

Medium · System Design & Object-Oriented Programm

Describe the Software Development Life Cycle (SDLC) phases and explain your preferred methodology when managing a fast-paced project.

Approach

  1. Fix the scope first: who calls this, how often, and what they do when it fails.
  2. Name the read and write paths separately; they rarely have the same bottleneck.
  3. Choose a partition key and say what query it makes expensive.
  4. State the consistency you need, and where you are willing to be stale.

Follow-up

  • What breaks first when traffic grows ten times?
  • How does this behave when that dependency is down for an hour?

How would you design a software architecture to handle real-time data streaming from multiple hardware sensors

Medium · System Design & Object-Oriented Programm

How would you design a software architecture to handle real-time data streaming from multiple hardware sensors on a drilling rig?

Approach

  1. Fix the scope first: who calls this, how often, and what they do when it fails.
  2. Name the read and write paths separately; they rarely have the same bottleneck.
  3. Choose a partition key and say what query it makes expensive.
  4. State the consistency you need, and where you are willing to be stale.

Follow-up

  • What breaks first when traffic grows ten times?
  • How does this behave when that dependency is down for an hour?

Describe how you would write and optimize a stored procedure to handle high-frequency data insertion.

Medium · Database & SQL

Approach

  1. Clarify what is being asked and what a complete answer contains.
  2. State your assumptions explicitly before working the problem.
  3. Say what you would check first and why it is the highest-information step.
  4. Work from the requirement backwards to the design.

Follow-up

  • What assumption would you test first?
  • How would you know your answer was wrong?

Explain a basic electrical circuit concept, including how you calculate voltage, current, resistance, and powe

Medium · Industrial & Hardware Integration

Explain a basic electrical circuit concept, including how you calculate voltage, current, resistance, and power.

Approach

  1. Say who the caller is and what they do when the call fails halfway.
  2. Define the identity of a request so a retry cannot double-apply it.
  3. Separate accepted, pending, failed and confirmed; they are different facts.
  4. Design the error taxonomy before the success shape; callers branch on it.

Follow-up

  • What happens if the caller retries after a timeout?
  • How does a client discover it is on an old version of this contract?

How would you approach writing software that must interface with a proprietary hardware tool or sensor?

Medium · Industrial & Hardware Integration

Approach

  1. Say who the caller is and what they do when the call fails halfway.
  2. Define the identity of a request so a retry cannot double-apply it.
  3. Separate accepted, pending, failed and confirmed; they are different facts.
  4. Design the error taxonomy before the success shape; callers branch on it.

Follow-up

  • What happens if the caller retries after a timeout?
  • How does a client discover it is on an old version of this contract?

Listing latency scales with page size, not with filters

Easy · n+1 · latency · query batching

The tenant listing endpoint reads resource filtered by tenant_id and status, ordered by updated_at DESC, and returns each row plus the owner's display name from app_user and the actor of that resource's latest resource_revision. p99 is 55 ms at 10 rows per page and 1.4 s at 200. Database telemetry shows 401 statements per request, each under 1 ms, and nothing in the slow-query log. Diagnose the cause and give the fix, stating the statement count per request and the p99 you expect afterwards.

Approach

  1. Read the counters before forming a theory. 401 statements for 200 rows is one driver query plus two per row, and sub-millisecond execution with an empty slow-query log rules out a bad plan. The time is round trips, which is why it is invisible in every per-query metric and scales with rows returned rather than with filter selectivity.
  2. Name the two per-row statements from their normalised text: a single-row app_user lookup by user_id, and a resource_revision lookup by resource_id ordered by version DESC LIMIT 1. Confirm by dropping those two response fields and watching the statement count fall to one. That locates the calls in the serialisation layer, not the repository.
  3. Check that the arithmetic accounts for the whole gap. Measure one round trip to the replica in isolation; 400 trips at roughly 3 ms of network plus 0.2 ms of execution is about 1.3 s on top of a 55 ms baseline, which matches. If the multiplication had fallen short, the N+1 would only be part of the story and you would keep looking.
  4. Batch both lookups. Collect owner_user_ids and resource_ids from the driver query, then issue WHERE tenant_id = $1 AND user_id = ANY($2) for the users, and PostgreSQL's SELECT DISTINCT ON (resource_id) ... WHERE resource_id = ANY($2) ORDER BY resource_id, version DESC for the latest revision, which the UNIQUE (resource_id, version) index serves directly. On an engine without DISTINCT ON, use a lateral join or a row_number window. Three statements per request at any page size.

Follow-up

  • The page size is capped at 200 today. What breaks first if it is raised to 2,000, and is it still this bug?
  • How do you stop the next N+1 from reaching production, given that no individual query is slow and the endpoint's tests pass?

Suggested practice checklist

Built from the rounds and topics National Oilwell Varco candidates report.

Day 1 — Map the National Oilwell Varco loop

  • Write out the reported sequence: Initial Screening, Technical Evaluation, Onsite / Panel Interview, Facility Tour & Wrap-up.
  • For each round, write one sentence on what it is judging, from the description above, and mark the one you are least ready for.

Deliverable: A one-page map of the 4 reported rounds, with the weakest marked.

Day 2 — Work Behavioral interview skills

  • Spend the session on Behavioral interview skills, which National Oilwell Varco candidates report being tested on.
  • Write one worked example in Behavioral interview skills and time yourself on it.

Deliverable: One timed worked example in Behavioral interview skills.

Day 3 — Work Communication skills (technical + interview communication)

  • Spend the session on Communication skills (technical + interview communication), which National Oilwell Varco candidates report being tested on.
  • Write one worked example in Communication skills (technical + interview communication) and time yourself on it.

Deliverable: One timed worked example in Communication skills (technical + interview communication).

Day 4 — Work Project experience storytelling

  • Spend the session on Project experience storytelling, which National Oilwell Varco candidates report being tested on.
  • Write one worked example in Project experience storytelling and time yourself on it.

Deliverable: One timed worked example in Project experience storytelling.

Day 5 — Answer out loud: Coding & Algorithms

  • Answer aloud, timed: Write a program that takes a list of numbers as input and outputs the missing numbers in the sequence (e.g., Input: [1, 2, 5, 7, 9], Output: [3, 4, 6, 8]).
  • Answer aloud, timed: Analyze a provided code snippet and determine the final value of a specific variable after execution.

Deliverable: Spoken answers to 2 reported Coding & Algorithms question(s), under time.

Day 6 — Answer out loud: System Design & Object-Oriented Programming (OOP)

  • Answer aloud, timed: Explain the core pillars of Object-Oriented Programming (OOP) and give a real-world example of how you have applied inheritance and polymorphism in a project.
  • Answer aloud, timed: What is the difference between a Web Service and Windows Communication Foundation (WCF)? When would you choose one over the other?

Deliverable: Spoken answers to 2 reported System Design & Object-Oriented Programming (OOP) question(s), under time.

Day 7 — Answer out loud: Database & SQL

  • Answer aloud, timed: Write a SQL Union Query to combine data from three tables sharing the same unique ID.
  • Answer aloud, timed: What is the difference between DROP, DELETE, and TRUNCATE tables in SQL? Explain the performance and transactional implications of each.

Deliverable: Spoken answers to 2 reported Database & SQL question(s), under time.

Behavioural preparation

Behavioural rounds judge the decision you made and what it cost.

Tell me about a time you had to learn a completely new programming language or technology on a very tight dead

Medium · Behavioral & Cultural Fit

Tell me about a time you had to learn a completely new programming language or technology on a very tight deadline. How did you approach it?

Approach

  1. Pick a story where you made the decision, not one where you watched it.
  2. State the situation in two sentences and spend the rest on the reasoning.
  3. Give the blast radius: what could have broken, and what you measured.
  4. Name the disagreement and how you resolved it with evidence.

Follow-up

  • What would you do differently if you ran that again?
  • How did you know your change caused the improvement?

Describe a situation where you had to work with a difficult team member or stakeholder. How did you resolve th

Medium · Behavioral & Cultural Fit

Describe a situation where you had to work with a difficult team member or stakeholder. How did you resolve the conflict to deliver the project?

Approach

  1. Pick a story where you made the decision, not one where you watched it.
  2. State the situation in two sentences and spend the rest on the reasoning.
  3. Give the blast radius: what could have broken, and what you measured.
  4. Name the disagreement and how you resolved it with evidence.

Follow-up

  • What would you do differently if you ran that again?
  • How did you know your change caused the improvement?

Why do you want to work for National Oilwell Varco, and what do you know about our role in the global energy i

Medium · Behavioral & Cultural Fit

Why do you want to work for National Oilwell Varco, and what do you know about our role in the global energy industry?

Approach

  1. Pick a story where you made the decision, not one where you watched it.
  2. State the situation in two sentences and spend the rest on the reasoning.
  3. Give the blast radius: what could have broken, and what you measured.
  4. Name the disagreement and how you resolved it with evidence.

Follow-up

  • What would you do differently if you ran that again?
  • How did you know your change caused the improvement?

How do you handle situations where technical requirements are ambiguous or change mid-project?

Medium · Behavioral & Cultural Fit

Approach

  1. Pick a story where you made the decision, not one where you watched it.
  2. State the situation in two sentences and spend the rest on the reasoning.
  3. Give the blast radius: what could have broken, and what you measured.
  4. Name the disagreement and how you resolved it with evidence.

Follow-up

  • What would you do differently if you ran that again?
  • How did you know your change caused the improvement?

Describe your experience, if any, with mechanical fundamentals or control systems (such as PLCs or SCADA syste

Medium · Industrial & Hardware Integration

Describe your experience, if any, with mechanical fundamentals or control systems (such as PLCs or SCADA systems).

Approach

  1. Pick a story where you made the decision, not one where you watched it.
  2. State the situation in two sentences and spend the rest on the reasoning.
  3. Give the blast radius: what could have broken, and what you measured.
  4. Name the disagreement and how you resolved it with evidence.

Follow-up

  • What would you do differently if you ran that again?
  • How did you know your change caused the improvement?