Interviewer view · keep this screen to yourself

Ethane cracker versus naphtha cracker

You run the case. Read the prompt, answer questions from the notes below, and share data only when the candidate asks for it or gets stuck. Score at the end.

Case timer

00:00

Target length:

1. Read the prompt aloud

Read it slowly, then pause. Let the candidate ask questions before they structure.

Compare two fictional ethylene producers. A Gulf producer uses ethane: 1.3 tonnes of ethane at USD 200 per tonne make 1 tonne of ethylene, plus USD 140 of other cash costs. A European producer uses naphtha: its net feedstock cost is USD 650 per tonne of ethylene after credits for the co-products it also sells, plus USD 150 of other cash costs. Ethylene sells for USD 950 per tonne. What is each producer's cash margin per tonne?

2. Answers to clarifying questions

This case has no scripted clarifying answers. Answer from the prompt, and say "assume what you think is reasonable" if the prompt does not cover it.

3. A model structure

Compare the candidate's structure with this one. A different split can be just as good if it is clean and fits the problem.

Cash margin = price minus (feedstock cost + other cash costs)
- Gulf: ethane used x ethane price + other costs
- Europe: net naphtha cost + other costs

4. The working, step by step

Each step shows how a strong candidate works it out. Share a new fact from it only when the candidate asks or is stuck, and let them do the math: the result in the dark box is what they should reach.

Step 1: Gulf cash cost
What a strong candidate does: 1.3 tonnes of ethane at 200, plus 140.
Gulf cash cost (USD per tonne of ethylene): 1.3 × 200 + 140 = 400
Step 2: Gulf cash margin
What a strong candidate does: Price 950 minus 400.
Gulf cash margin (USD per tonne): 950 - (1.3 × 200 + 140) = 550
Step 3: Europe cash cost
What a strong candidate does: Net naphtha 650 plus 150.
Europe cash cost (USD per tonne of ethylene): 650 + 150 = 800
Step 4: Europe cash margin
What a strong candidate does: Price 950 minus 800.
Europe cash margin (USD per tonne): 950 - (650 + 150) = 150

The recommendation to listen for

At the end, say: "The CEO walks in. What is your recommendation?"

New capacity should go where feedstock is cheap, because the Gulf ethane producer earns about USD 550 per tonne against USD 150 for the European naphtha producer. First, the Gulf cash cost is USD 400 per tonne against USD 800 in Europe. Second, this means that if ethylene falls below USD 800, the European producer loses cash while the Gulf producer still earns well. The risk is that ethane supply is limited, and naphtha co-products can narrow the gap in some years. As a next step, test both margins across a range of ethylene prices.

Risks a strong answer names: Ethane is not always available in large amounts; some Gulf producers also use propane or naphtha; Naphtha crackers produce more valuable co-products, which can narrow the gap in some years.

Score the candidate

Score each criterion from 1 to 5. A 2 or a 4 sits between the descriptions.

This case has no exhibit. Score Exhibit reading on how the candidate used the data you gave them: did they pick out the number that matters and say what it means?

Structuring

1: No clear structure, or a memorized framework that does not fit the problem.
3: A sensible structure, but with some overlap, a gap, or no clear priority.
5: A structure built for this problem, with no overlap and no gaps, a stated hypothesis, and a clear first step.

Math

1: Frequent errors, no units, or needed heavy help to finish.
3: Right answers but slow or messy working, or one error caught late.
5: Accurate and clearly narrated, with units, a sense check, and what the number means.

Exhibit reading

1: Read the chart aloud without finding the number that matters.
3: Found the key number but gave only part of the so-what.
5: Pulled the right number quickly and said what it means for the case.

Synthesis

1: Summarized what was done, with no clear answer.
3: Gave an answer, but with weak reasons or no next step.
5: Answer first, then two or three reasons with numbers, the main risk, and next steps.

Communication

1: Hard to follow: long silences, no signposting.
3: Clear most of the time, with some rambling.
5: Calm and concise, signposted each step, and checked in with the interviewer.

Total

0 out of 25

Score all five criteria to see the band and the feedback template.