US regulators have granted tentative approval for three fund providers to begin offering actively managed exchange traded funds as the mutual fund industry awaits the expected entrance of the controversial new type of investment vehicle.

ETFs, which like stocks can be bought and sold throughout trading days on public exchanges, typically track an index passively through a basket of securities and cannot choose other individual investments. But last Friday the Securities and Exchange Commission exempted Invesco’s Powershares Capital Management from rules that prevent ETFs from making trades.