Who trades at the close? Implications for price discovery and liquidity

Closing auctions set daily closing prices for U.S. stocks and account for a striking 7.5% of daily volume in 2018, up from 3.1% in 2010. We study closing auctions in the new regime of record volume. Closing auctions appear to match volumes at low cost: closing prices typically match pre-close bid or ask prices, and price impact is lower than during continuous trading. Auction price deviations revert quickly and almost completely, on average. Auction-to-intraday volume spikes on S&P 500 additions and increases permanently afterwards, suggesting that closing volume is fueled directly and indirectly by the growth of indexing and ETFs.