Vanguard and iShares are no longer the lowest cost ETF providers in the market. State Street, the third largest ETF provider after Vanguard and iShares, has joined the pack. On Monday it announced big cuts in the expense ratios of 15 SPDR ETFs to levels at or below the lowest in the industry and the formation of SPDR Portfolios ETFs, which contain those 15 ETFs.

“Investors have been asking us to provide these solutions to offer them a greater choice for low-cost ETFs,” said Nick Good, co-head of the Global SPDR business at State Street Global Advisors (SSGA), in a statement. “The launch of the SPDR Portfolio ETFs provides a solution that meets this growing demand.”

The SDPR Portfolio ETFs comprises 15 existing funds, including three that will track new indexes, and all are available for purchase commission-free on TD Ameritrade’s new ETF Market Center starting Tuesday. The dozen other ETFs have all been renamed as an “SPDR Portfolio.”

Related: TD Ameritrade Is Nearly Tripling Its Commission-Free ETF Offerings)

“Investors seem to gravitate toward lower cost products,” said Todd Rosenbluth, director of ETF and mutual fund research at CFRA. “State Street is now fighting for more market share. It was a long time coming. Fees were in many cases highly expensive and not well suited to a fee-based approach.”

(Related: Schwab Announces Lower Cost ETF for 1,000 Largest US Stocks)

Not anymore. The SPDR Portfolio S&P 500 Growth ETF (SPYG), which used to charge an expense fee of 15 basis points, now charges four, the same as Vanguard. Its emerging markets ETF (SPEM) charges 11 basis points, a fraction of the 59 basis points it used to charge, and less than the 14 basis points cost for emerging market ETFs from Vanguard and iShares.

(Related: Goldman Starts Smart Beta ETF Price War)

“Research has long shown that asset allocation decisions explain over 90% of the variance in portfolio returns,” said Matt Bartolini, head of SPDR Americas Research, in the statement. “Simply put it all starts with asset allocation. And today’s low return expectations make an ultra-low-cost, diversified core more important than ever, as costs accumulate over time, eroding a portfolio’s total return.”

(Related: Fund Expenses Drop 7% in 2016; Vanguard Leads the Pack: Morningstar)

Rosenbluth agrees that investors will now have more low-cost choices when building their asset allocation portfolios, but he cautioned against blindly going with the cheapest ETF.

State Street’s SPYG ETF has historically traded less frequently than comparable Vanguard and iShares ETFs, leading to bigger bid/ask spreads, which can involve increased trading costs, said Rosenbluth. Those spreads should narrow with the new, lower expense ratios but it’s not clear yet by how much.

In addition, said Rosenbluth, ETFs in the same category are not necessarily identical because they may track different indexes. State Street’s emerging markets ETF (SPEM), for example, tracks the S&P Emerging BMI Index, while the Vanguard Emerging Markets Index ETF (VWO) tracks the FTSE Emerging Markets All Cap China A Inclusion Index, and the iShares Core Emerging Markets ETF tracks the MSCI Emerging Markets Investable Market Index Benchmark Index.

As part of Monday’s ETF announcement, State Street will be replacing the underlying indexes for three stock market ETFs, substituting its own proprietary SSGA indexes for indexes from FTSE Russell, starting Nov. 16.

They are the SPDR Total Stock market ETF (SPTM), which will use the SSGA Total Stock Market Index instead of the Russell 300 Index; the SPDR Large Cap ETF (SPLG), which will be substitute the SSGA Large Cap Index for the Russell 1000 Index; and the SPDR Small Cap ETF, to be based on the SSGA Small Cap Index instead of the Russell 2000 Index.

The lower expense ratios for these funds, however, took effect Monday.

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