Under what scenarios could arbitrage opportunities exist in todayâs equity markets? I know arb trading isnât for the small guys but I'm just curious if and when is it happening? The only example I can think of is in a scenario where 2 ECN's are listing the same stock and a large buy or sell order comes into one of the ECN's and before the order is printed on the tape the ECN starts to reprice the stock based on the buy/sell order that came in? And someone connected to both ECNâs could see the inconsistency between the prices of this stock and issue a buy/sell or visa versa on both ECNâs? Would this be a valid scenario? Does this still happen today?