At the same time, Vanguard’s market share climbed 250 basis points to 25.2%. The firm’s largest offering, Vanguard Total Stock Market ETF (VTI) now has $127 billion in assets, up 62% from the end of 3Q 2017. Meanwhile, Vanguard S&P 500 ETF (VOO) more than doubled in size to $73 billion; VTI holds small, mid and large-cap stocks, while VOO and peer IVV focus only on large caps.

Related: How to Determine if Smart Beta ETFs Fit in Your Portfolio

CFRA thinks the ETF market will continue to expand, creating opportunities for various firms to gather assets. However, the “big three” have scale and brand advantages that make taking share from them it a challenge. Indeed, various media reports, including Bloomberg, suggest that Invesco PowerShares is in talks to acquire Guggenheim. While both firms have top-10 asset bases, their combined 5.3% market share is down from 5.9% nearly two years ago.

Todd Rosenbluth is Director of ETF & Mutual Fund Research at CFRA.

For more information on the ETF market, visit our ETF performance reports category.