Exchanged traded funds have enjoyed great popularity recently, raising concerns in some quarters that they may be introducing froth to equities markets.  But not everyone is convinced. With other asset classes seeing upticks in inflows, bulls argue there is a lot more room for ETFs to run, boding well for ETF providers.

Citing data from Goldman Sachs, Marketwatch reported that around 6% of the corporate equity market is held by ETF investors, underscoring a rapid adoption rate for an investment that has only been around for a quarter century. According to Toroso Investments, ETFs represented just 2.25% of the equity markets back in 2012. When compared to other investments, ETFs are still small. MarketWatch found that mutual funds are held by 24% of the market while international investors hold 15% of corporate stocks. Meanwhile, households in the U.S. own 37% of the corporate equity market. Because of their relative size compared to other investment types, Toroso Investments is among those that don’t think ETFs are in bubble territory.

For the six months of the year ending in June, ETF inflows have jumped to $249.4 billion, nearing the $287.5 billion added for all of 2016, according to Total assets under management for U.S. based ETFs is now at slightly under $3 trillion.  In June alone $45.5 billion of new inflows came to ETFs.

For discount brokers, particularly Charles Schwab, a continuation of the record-setting performance in ETFs means more potential chances to make money. While the San Francisco discount broker is behind rivals when it comes to selling ETFs, it has been increasing efforts to become a leading player, just recently rolling out a new low-cost ETF that has an operating expense ratio of 5 basis points of 0.05%. The new fund started trading on Oct. 11 and is available via Schwab's commission-free ETF program. Charles Schwab said in the announcement the expense ratio is one-half to one-third cheaper than other ETFs that track the biggest 1,000 U.S. stocks. It currently offers 22 low-cost ETFs and its commission-free ETFs number in the 200 range. According to Investor’s Business Daily, Schwab ETF OneSource program has brought in $18 billion in new ETF flow in 2017 alone, accounting for 51% of its total ETF flow.

Meanwhile, E*Trade, the New York discount brokerage, has also been beefing up its commission-free ETFs, adding 68 so far in 2017, according to Barron’s. That brings the total to 149 ETFs that are non-proprietary and are free of commissions. With trading commissions being slashed amid a price war among discount brokers, ETFs provide a way to make money. In an environment where there is more demand for ETFs that means more revenue to share.