Oliver Wyman cases: turn analysis into a decision.

Oliver Wyman tells candidates to pinpoint the issue and explain their understanding before moving into analysis. Practise doing that with this original exercise:

A charging operator wants to serve electric vehicles in a small city. How much charging capacity should it install?

Clarify what you are sizing. Is the operator serving the entire city's public charging demand, one neighbourhood or a proposed site? Does the question concern charging ports, locations or investment cost?

Suppose the interviewer defines the task as enough ports across the city for expected public charging visits. Locations and grid constraints come later. You can now state the first analytical question: how many visits must the network handle, and when do they arrive?

That short exchange demonstrates the firm's published advice to ask the right questions and agree on an approach. It is more useful than launching straight into a population calculation.

Use these fictional planning assumptions:

There are 6,000 public-charging users and 12,000 visits per week. Spread evenly across seven days, that is approximately 1,714 visits per day.

A port open for twelve hours could serve 24 half-hour visits if it operated continuously with no gaps. Dividing 1,714 by 24 gives about 71.4, so 72 ports is the rounded theoretical requirement under evenly distributed demand.

Say the condition with the result:

“The daily average implies 72 ports if use is spread evenly and every slot is filled. I would now check the busiest period because the average may hide the actual capacity requirement.”

This moves the case forward. You have produced a first estimate and identified the assumption most likely to make it insufficient.

The interviewer now tells you that 60% of visits happen during a four-hour evening window. Assume visits are evenly distributed across those four hours for this calculation.

Peak demand is approximately 1,029 visits: 60% of 1,714. Each port can handle eight half-hour visits in that window. The network therefore needs approximately 129 ports to cover the peak at continuous occupancy.

Your first estimate would be substantially too small, even though it was arithmetically correct.

If the operator uses 80% of theoretical capacity as a planning assumption to allow some slack, a port supplies 6.4 effective slots during the peak. Peak demand divided by 6.4 gives approximately 161 ports, rounded up.

Be precise about what that means. The 80% assumption creates a capacity allowance; it does not prove that a particular waiting-time target will be met. Arrival patterns, charging durations and how demand is distributed across sites still matter.

At this stage, you can give a provisional planning answer:

“I would plan around peak demand. The stated assumptions imply roughly 129 ports at full use, or 161 with our 80% planning utilisation. Before committing, I would test where those visits occur and whether each site has the power and space to serve them.”

The network total does not establish a site plan. One busy location can have queues while another sits empty. A technically suitable site can also be commercially unattractive if its connection cost or rent is too high.

You can organise the next decision around three questions: which locations capture the demand, which can supply the required service, and which earn an acceptable return after installation and operating costs?

That is a useful commercial structure because each question can eliminate a proposed site. “Market, competition and company” is less helpful until you explain what you intend to decide within each heading.

Oliver Wyman's preparation guide explicitly frames the interviewer as someone to work with, not an adversary withholding the answer. In this exercise, imagine being asked: “Could pricing reduce the investment needed?”

Explore the mechanism. A lower off-peak price might shift flexible visits out of the evening window. It might instead attract additional visits and reduce revenue per visit without relieving the peak.

Ask which users can change charging times, what price difference could affect behaviour and what evidence would show whether visits moved. Then calculate how much peak demand must shift to avoid a block of new ports. You are improving the capacity decision together, not defending the first estimate at all costs.

The firm's published conversational-interview guidance covers your accomplishments, experiences, interests and career objectives. Prepare that discussion separately from the case rather than assuming a strong calculation will answer every question.

Choose a business development you can discuss beyond the headline. Explain which customer behaviour is changing, which companies benefit, what could go wrong and which fact you would check next. The charging example supplies a pattern: attractive demand does not guarantee good economics at each site.

For your own experience, select a decision that reveals initiative, judgement and collaboration. Be ready to explain an alternative you rejected and why. A detailed account helps the interviewer understand how you work.

Start with Oliver Wyman's official preparation page and its WumbleWorld and Aqualine practice cases. Then try an unfamiliar case aloud so you cannot rely on a remembered answer. Confirm the format for your office and role, including whether written analysis or a presentation is involved.

Ask your partner to introduce a fact that changes an important assumption. Pause, update the calculation and state the implication in a sentence. Review whether the recommendation improved, not whether you preserved your first answer.

For another estimation exercise, use the market-sizing examples. Then use the case library for a different industry. Keep asking what decision each number now allows the client to make.