Market executives called for an overhaul of stock market trading rules in a US Senate hearing Tuesday, saying the shift to high-frequency and off-exchange trading has created too much complexity that favors the most sophisticated investors.

The hearing, the second by the Senate Banking Committee on computer-driven trading in the past month, comes amid heightened scrutiny of off-exchange venues such as dark pools and high-frequency trading, which accounts for about half of all trading in US stocks.