No. 72 2 min read
One book, fourteen venues
Fragmentation gets blamed for a lot. Most of what it is accused of is really the cost of stitching separate books back together in real time.
Last week the argument was that a quote is an option. This week: what happens when the same instrument is quoted in a dozen places at once, by participants who cannot all see each other at the same instant.
Fragmentation is usually discussed as though it were a policy mistake. It is more useful to treat it as a physics problem that policy then has to live with.
The consolidated book is a fiction you compute
There is no single book. There are many books, each maintained by a venue that knows only its own state, publishing updates that arrive at every other participant at different times.
The “national best bid and offer”, or whatever your jurisdiction calls it, is not a thing that exists somewhere. It is a number each participant calculates from the messages they have received so far. Two participants with different connectivity compute different values for it at the same wall-clock instant, and both are correct given what they know.
Everything awkward about fragmented markets follows from that.
Latency is not a speed problem
The usual framing is that fast participants beat slow ones to the trade. True, but it undersells it.
The real asymmetry is that a fast participant knows the state of the market sooner. If venue A trades at 100.90 and you are quoting 100.85 bid on venue B, your quote is now stale — not wrong when you posted it, but wrong now — and the question is only whether you learn that before someone acts on it.
That is the option from last week, with a new expiry: the time it takes news of one venue to reach another. Shorten it and quotes tighten. Lengthen it and every resting order across every venue must be priced for a longer window of ignorance.
Fragmentation does not create the adverse-selection problem. It sets the clock on it.
What it actually costs
Three costs, in rough order of how much they are talked about versus how much they matter:
| Cost | Borne by | Talked about |
|---|---|---|
| Connectivity and market data | Intermediaries | Constantly |
| Stale-quote risk across venues | Liquidity providers | Sometimes |
| Complexity of proving best execution | Everyone | Rarely, and reluctantly |
The first is a real expense and shows up in fee schedules, which is why it dominates the discussion. The second is priced into every spread you have ever paid and appears on no invoice. The third is the one that quietly shapes how brokers route, because a routing decision that is hard to defend afterwards is a routing decision that does not get made.
The case for it anyway
Given all that, why not consolidate?
Because a single venue is a single point of failure, a single fee schedule, and a single operator with no particular reason to improve. Competition between venues is what produced continuous matching, sub-penny economics, and the operational reliability that fragmented markets are rarely credited with. The costs above are real. They are also the price of not having one owner of the only door.
The honest summary is that fragmentation trades a visible, measurable cost for an invisible, structural benefit — which is exactly the trade that markets are worst at defending in public.
Next week: settlement, and the two days where none of the above applies.