Quick definition The best bid-offer (BBO) is the highest bid and lowest ask available across all trading venues for a given security. It represents the best price available to buy or sell at that moment. What it is In US equity markets, trading occurs on multiple venues simultaneously: NYSE, NASDAQ, CBOE, and electronic networks like Arca. Each has its own order book. The BBO is the highest bid price across all venues and the lowest ask price across all venues. For example, at 10:32 AM: - NYSE shows bid 156.42 / ask 156.43 - NASDAQ shows bid 156.40 / ask 156.44 The BBO is bid 156.42 (best from NYSE) and ask 156.43 (also from NYSE). Why it matters Brokers are required to route customer orders to get the BBO or better. Consistently missing the BBO on customer orders creates regulatory liability. The BBO also determines certain regulatory limits; for example, short sales under Regulation SHO must occur at or above the best bid. BBO versus Top-of-Book Top-of-book refers to the best bid and ask on a single venue. The BBO is the best bid and ask across all venues. In fragmented markets, they can differ. Practical example You want to buy 50,000 shares. The BBO is bid 429.80, ask 429.85 (spread of 0.05 dollars). Your broker routes you to the venue showing the best ask at 429.85. If routed to a different venue with an ask of 429.90, you overpay by 0.05 dollars per share, losing 2,500 dollars in value. This is why best execution is monitored. Consolidated feeds The BBO is published in real time by SIP (Securities Information Processor) feeds. All market participants can see the same BBO, ensuring fair access to best prices. Clock synchronisation across venues is imperfect, so BBO updates may lag slightly. See also - National Best Bid-Offer (NBBO) - Bid-Ask Spread - Order Book - Venue - Securities Information Processor (SIP)
