Key takeaways
- Aggregation merges many separate provider feeds into one consolidated order book with a single best bid and best offer.
- The engine normalises each feed, sorts prices by level, and stacks depth from multiple sources behind the top of book.
- Smart order routing then sends each order to the source — or combination of sources — that produces the best fill.
- The benefits are greater depth, a tighter effective spread and resilience when a single source widens or drops out.
- A Prime of Prime runs this aggregation on its own bank relationships, so clients connect once and trade the blended book.
What liquidity aggregation is
In FX there is no single central exchange. Prices are quoted independently by many venues — tier 1 banks, non-bank market makers, ECNs and other liquidity pools — and each shows only its own bids, offers and depth. Liquidity aggregation is the technology layer that collects those separate feeds in real time and combines them into one order book that behaves as if it came from a single, much larger source.
The aggregated book carries a consolidated best bid and best offer (the highest price a buyer is quoting and the lowest price a seller is quoting across all sources), with the remaining prices from every feed stacked behind it as depth. A trading desk sees and trades one book; underneath, that book is assembled continuously from many providers.
How multiple feeds become one book
Feeds arrive in different formats, at different speeds, and with different conventions. Turning them into a usable single book happens in a few stages:
- Ingest & normalise. Each provider’s feed is received (typically over FIX or a native API) and translated into a common internal format — same symbols, same price and size conventions, timestamped on arrival.
- Validate. Stale, crossed or obviously erroneous quotes are filtered so bad prices do not pollute the book.
- Sort into a consolidated book. All valid bids are ranked highest-to-lowest and all offers lowest-to-highest, so the best prices sit at the top and the rest form the depth ladder below.
- Publish top of book & depth. The engine publishes a single best bid/offer plus aggregated depth that the desk, GUI or API consumes as one feed.
Because the book refreshes continuously, the top of book always reflects whichever provider is currently pricing best on each side — which may be a different source for the bid than for the offer.
Smart order routing and best execution
Aggregation builds the book; smart order routing (SOR) decides where an order actually goes. When a client sends an order, the router looks at the live aggregated book and directs the order to the source offering the best price for the required size. If a single source cannot fill the whole order at the top level, the router can sweep across multiple sources and price levels to complete the fill, taking the best available liquidity in sequence.
Running full straight-through processing, the routed orders pass to the underlying venues with no dealing desk taking the other side — so fills and pricing are something a client can reconcile. You can read more about how this is delivered on our execution and technology pages.
A structural illustration
The table below is a structural example only — it shows which source is best on each side, not any specific prices or spreads. In this illustration three feeds are quoting the same pair, and the aggregator builds the top of book from whichever feed is best on each side.
| Source | Best on the bid? | Best on the offer? | Role in the book |
|---|---|---|---|
| Bank feed A | Yes — top bid | No | Sets the consolidated bid |
| Bank feed B | No | Yes — top offer | Sets the consolidated offer |
| Non-bank feed C | No | No | Adds depth behind the top of book |
Illustrative and structural. No prices or spreads are shown or implied; which source is best changes continuously in live markets.
The key point: the consolidated best bid and best offer can come from different providers at the same instant, and the effective spread the client trades is the distance between them — typically tighter than any single source could show alone.
Why aggregation matters
- Depth. Stacking multiple sources means larger orders can be filled without walking as far down a single provider’s ladder.
- Tighter effective spread. Always surfacing the best bid and best offer across sources compresses the spread the desk actually trades.
- Resilience. If one provider widens, lags or drops out, the others keep quoting and the book stays usable — important in fast or stressed markets.
- Choice and neutrality. A blended book is not dependent on any one price maker, reducing single-source bias.
How a Prime of Prime fits
Assembling this yourself means holding relationships with each provider, ingesting every feed, and running the aggregation and routing engine — a significant undertaking. A Prime of Prime does it on your behalf: it holds the tier 1 bank relationships, connects the non-bank venues, aggregates the feeds into one book, applies credit and risk controls, and lets clients connect a single time. That is the essence of the model — one aggregated liquidity feed, delivered over FIX or a bridge, instead of many bilateral connections.
For definitions of the terms used here, see the glossary. For the related question of how providers accept or reject the orders routed to them, see what is last look in FX.
Frequently asked questions
What is a liquidity aggregator?
A liquidity aggregator is technology that collects price feeds from multiple liquidity providers — tier 1 banks, non-bank market makers, ECNs and other venues — and consolidates them into a single order book. It sorts every incoming bid and offer by price, presents the best available prices at the top of book, and can route orders to whichever source offers the best fill. The result is one deep, blended feed instead of many separate connections.
Why aggregate liquidity from multiple providers?
Aggregating multiple providers deepens the available liquidity, tightens the effective spread by always surfacing the best bid and offer, and adds resilience — if one source widens or drops out, others continue to quote. A single provider can only show its own prices and its own depth; a blended book combines many sources so the order book stays usable in both calm and stressed markets.
How does a Prime of Prime aggregate liquidity?
A Prime of Prime holds prime brokerage relationships with tier 1 banks and connects to non-bank venues, then runs an aggregation engine that normalises those feeds, builds a consolidated best bid and offer, applies credit and risk parameters, and routes orders straight through to the underlying sources. Clients connect once — by FIX API or a platform bridge — and trade the single aggregated book instead of managing many bilateral relationships. Talk to our desk to learn more.