An arbitrage game for trading interviews
Some trading firms, Optiver among them, test whether you can look at a wall of quotes and instantly see the one trade that cannot lose. This free browser game trains exactly that: a board of two-sided markets on gold, silver, copper, platinum and oil, one hidden risk-free combination, and a clock. Buy the cheap side, sell the rich side, leave your inventory flat, keep the cash.
An arbitrage is a set of trades that ends with zero net position in every asset yet a positive cash balance: profit with no risk. Real desks live and die on spotting these before anyone else. On each card, SELL is the price you receive for selling that bundle into the market and BUY is the price you pay to buy from it, and because SELL is always below BUY, no single card is ever a free trade. The edge only appears when you combine cards.
A worked example
Say the board hides this trade. One card is a bundle of gold plus silver, quoted SELL 8 / BUY 9. Another is gold plus copper, quoted SELL 9 / BUY 10. A third card, priced a touch too generously, is a two-gold-plus-silver-plus-copper bundle quoting SELL 20 / BUY 22. Buy the first two bundles, paying 9 and 10, for 19. Sell the big bundle into the third card for 20. Your gold, silver and copper all net to zero and you are up 1, risk-free. That plus-one is the whole point: a small guaranteed profit beats a big gamble, and the game rewards finding the trade, not sizing it. Later boards make the gap thinner and force you to buy two of a card, or combine three or four bundles across every metal.
The skills it drills
- Reading a two-sided market. Bid and ask on every quote, and the instinct that you buy at the ask and sell at the bid.
- Replication. A bundle is worth the sum of its parts. When the market prices the whole differently from the pieces, that gap is free money.
- Staying flat. An arbitrage is only risk-free if your inventory in every commodity nets to zero. There is no running tally: you total the book in your head, exam-style, and only the final scorecard tells you how many you nailed.
- Ignoring the noise. Several cards on each board are decoys that look tempting but never help. Later rounds add lookalike quotes that are priced just a hair worse than the one you actually need.
It is the natural next step after the market making game: there you quote a market and manage risk, here you hunt the mispricing that a careless market maker left behind. Both reward the same fast, structured pricing sense that trading interviews are built around.