Investors allocated $73.5 billion to U.S.-listed exchange-traded funds in the first half, according to a report by ETF.com.

Approximately two-thirds of that amount poured into equities, amid optimism about U.S. economic recovery.

The report said total ETF assets listed in the U.S. at the end of June stood at $1.9 trillion, nearly 7 percent higher than at the end of 2013 and 26 percent higher than the year-earlier period.

The asset growth reflected a nearly 6 percent increase in the S&P 500 index.

The report noted that this year’s asset gathering has so far lagged the pace needed to match the one-year inflow record of $189 billion set last year.

Still, that was not out of the question, as inflows appeared to be accelerating. In June, they topped $25 billion, according to the report.

ETF.com’s data showed that the top gainers in the first half were the following:

1. Vanguard: Vanguard FTSE Developed Markets (VEA)—$3.9 billion

2. Vanguard: Vanguard REIT (VNQ)—$3.4 billion

3. State Street Global Advisors: Energy Select SPDR (XLE)—$3.3 billion

4. Vanguard: Vanguard S&P 500 (VOO)—$3.3 billion

5. Vanguard: Vanguard FTSE Europe (VGK)—$3.2 billion

6. Vanguard: Vanguard Total Stock Market (VTI)—$2.9 billion

7. BlackRock: iShares MSCI EMU (EZU)—$2.7 billion

8. BlackRock: iShares 7–10 Year Treasury Bond (IEF)—$2.5 billion

9. Vanguard: Vanguard Total Bond Market (BND)—$2.3 billion

10. BlackRock: iShares MSCI EAFE (EFA)—$2 billion

ETF.com said Vanguard attracted more than any other ETF sponsor in the first half, almost $31 billion.

The report said the firm’s low-cost pure-beta funds, which typically employ capitalization-weighted indexes, were still attracting serious attention, even as smart-beta index funds designed to beat cap-weighted indexes gained a bigger following in the world of ETFs.

Smart-beta funds’ ascendancy notwithstanding, debate exists on whether there’s a better beta.

The report also noted that with $384 billion in assets under management, Vanguard was within striking distance of catching and surpassing the No. 2 ETF firm, State Street Global Advisors, which has $403 billion.

BlackRock remains top dog, with $718 billion in assets.

Following are the ETFs with the biggest first-half outflows, according to ETF.com data:

1. State Street Global Advisors: SPDR S&P 500 (SPY)—$14.7 billion

2. Invesco PowerShares: PowerShares QQQ (QQQ)—$4.2 billion

3. State Street Global Advisors: Consumer Discretionary Select SPDR (XLY)—$2.3 billion

4. Vanguard: Vanguard FTSE (VWO)—$2.3 billion

5. BlackRock: iShares Russell 2000 (IWM)—$2.3 billion

6. Van Eck: Market Vectors Agribusiness (MOO)—$2.2 billion

7. WisdomTree: WisdomTree Japan Hedged Equity (DXJ)—$1.7 billion

8. BlackRock: iShares iBoxx $ High Yield Corporate Bond (HYG)—$1.6 billion

9. BlackRock: iShares MSCI Emerging Markets (EEM)—$1.5 billion

10. State Street Global Advisors: Technology Select SPDR (XLK)—$1.4 billion