Trading firms
Who fills your order?
A handful of trading firms (market makers) fill most retail orders and set the price you get.
Market orders fill at once; marketable limit orders add a price cap.Apex routes orders for several brokers; you can't open an account there.
Trading firms used
29
by brokers here, Apr–Jun 2026
Trading firms compared
8
on identical S&P 500 trades, September 2026
Biggest by volume, Q3 '26
28%
Citadel's off-exchange share
Who sends orders where
S&P 500 · Apr–Jun 2026 · share of orders · click a broker
Price quality on the same stocksA trading firm's score mixes its own pricing with the brokers that send it orders.
S&P 500 · market orders · points of the spread vs other firms
Share of off-exchange stock trading
FINRA volume data · full quarters