OTC desk or exchange: when a block trade is the right call
Key takeaways
- Below the point where your order would move the book, an exchange is cheaper and safer; above it, the visible spread stops being the real cost.
- The real comparison is exchange slippage plus fees plus market impact, against the OTC spread plus counterparty risk plus settlement time.
- Signalling matters as much as slippage: a large resting order tells the market what you are doing before you have finished doing it.
- OTC introduces counterparty and settlement risk that an exchange absorbs — which is why procedure, not price, is where OTC deals are won or lost.
The question is usually framed as a preference. It is not: it is arithmetic with a term that most people leave out.
The comparison people make
The visible spread on an exchange is tight, and the OTC quote carries a wider one. On that basis the exchange always wins, and for ordinary size it does.
The comparison that is actually true
Above a certain size, the visible spread is not the price you get. The real exchange cost is:
- Slippage — how far your order walks the book to fill.
- Fees — taker fees on the full notional.
- Market impact — the price move your own order causes, which you then trade against for the remainder.
- Signalling — what a large resting order or a visible pattern of fills tells everyone watching.
The real OTC cost is the quoted spread, plus counterparty risk, plus the time and effort of settlement. When the first list exceeds the second, the block trade is cheaper — and the crossover point depends entirely on the depth of the particular book at the particular moment, not on a threshold someone quoted you.
Signalling is underrated
Slippage is a cost you can measure afterwards. Signalling is a cost you often cannot: a treasury accumulating over weeks on a public book teaches the market its size, its cadence and its price tolerance. OTC settlement stays off the public order book, which is frequently the reason institutions use it even when the arithmetic on slippage alone is marginal.
What you take on instead
An exchange is, among other things, a counterparty risk absorber: it guarantees the other side of your fill. Trading bilaterally removes that guarantee and hands the risk to you. This is why every serious OTC procedure is built around managing it — proof of control before the first transfer, tranche settlement that limits exposure at each step, and an escrow agent where the size or the jurisdictions warrant one.
The practical test
- Take your intended size and measure the slippage against current resting depth.
- Add taker fees on the full notional.
- Add a realistic estimate of impact for the portion you would trade after moving the price.
- Compare the total to the OTC spread you can actually get quoted — not a hypothetical one.
- If the numbers are close, decide on signalling: does it matter whether the market sees this?
Run that once for your typical ticket and you will know where your own line sits, which is more useful than any figure a broker offers you.
Questions this answers
- At what size should I use an OTC desk instead of an exchange?
- There is no fixed number: it depends on the depth of the specific book at the moment you trade. The practical test is to measure the slippage your order would incur against the resting depth, add fees and the market impact of showing size, and compare that to the OTC spread you are quoted. When the first number exceeds the second, OTC is cheaper.
- Is OTC trading safer than an exchange?
- It trades one risk for another. An exchange absorbs counterparty and settlement risk but exposes you to slippage and signalling. OTC removes both of those and hands you counterparty risk to manage yourself — through proof of control, tranche settlement and, where warranted, escrow.
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