[ESMA 70-872942901-38 MiFID II MiFIR market structures Q&A, Q&A 3.18]

As clarified by Recital 3 of Commission Delegated Regulation (EU) 2017/566 (RTS 9) trading venues may set the maximum ratio of unexecuted orders to transactions at the level they consider appropriate to prevent excessive volatility in the financial instrument concerned.

Nothing prevents trading venues from setting the limits on the basis of the different categories of market participants that operate in their systems. In particular, trading venues may determine a specific limit ratio for members or participants subject to market making obligations under a written agreement (Article 17(2) of MiFID II) or a market making scheme (Article 48(2)(b) of MiFID II).

The ratio limiting the number of unexecuted orders to transactions should be set in compliance with the objective of Article 48 of MiFID II and supported by statistical analysis of the activity of the different categories of members or participants and the liquidity of the instruments in which they operate.