Odd Lot Transparency
Odd lot transparency refers to the inclusion of orders and quotes involving fewer than 100 shares (odd lots) in consolidated market data feeds, a reform that became effective in 2023 under updated SEC market data rules.
An odd lot is any order or trade involving fewer than 100 shares. For most of US equity market history, odd lot quotes were not included in the National Best Bid and Offer and were invisible in consolidated market data. Only round-lot quotes — orders for 100 or more shares — were protected under Regulation NMS and included in the NBBO calculation.
This created a meaningful blind spot. As stock prices climbed — particularly for high-priced shares like Amazon, Google, and Berkshire Hathaway Class A — a substantial portion of trading activity occurred in odd lots. Retail investors trading single shares, and institutions transacting in fractional shares, generated order flow that simply did not appear in the official quote data. Sophisticated participants with access to proprietary exchange data feeds could observe this activity; participants relying only on consolidated data could not.
The SEC addressed this asymmetry in its 2020 market data infrastructure rules and subsequent amendments, requiring exchanges to include odd lot quotes in the consolidated SIP feeds. Under the revised rules, the best odd-lot bid and offer — even if fewer than 100 shares — must be included in consolidated data when they represent a better price than the best round-lot quote. This effectively expanded the NBBO to reflect a more complete picture of available liquidity.
The practical effect is most significant in high-priced stocks. A stock trading at $3,000 per share may have the majority of its best-priced quotes in the odd-lot tier, since committing 100 shares requires $300,000 in capital. Before the reform, the official NBBO in such stocks could be materially wider than the actual best available price. After the reform, the consolidated data better reflects where trades can actually occur.
Odd lot transparency is viewed as a pro-competition measure that levels the informational playing field between firms paying for proprietary data and those relying on consolidated feeds.