The ETF industry has been roaring with explosive growth thanks to unique strategies, creativity, transparency, diversification benefits, enhanced tax competences, low turnover and low cost.In particular, investors seek to trade in ETFs that can easily be purchased and sold on the market, suggesting that the fund should have enough liquidity. Volume, or the number of shares traded in a particular period, is definitely the most important determinant of the liquidity of a particular fund. A higher number of shares provides easy access to move in and out of the product, keeping the bid/ask spread tight.Further, greater volume ensures easy creation and redemption of shares in the fund basket, which is a regular and vital mechanism in the ETF. This is especially true as authorized participants (AP) have the ability to create new baskets of ETFs for underlying securities or redeem them when required. This phenomenon allows ETFs to trade in line with their net asset value (NAV) (see: all the Category ETFs here).That said, we have highlighted 10 ETFs that have seen massive trading volumes and are the top 10 volume leaders of 2Q, as per etfdb.com.Financial Select Sector SPDR Fund XLFThe fund targets the broad financial segment and follows the Financial Select Sector Index. It holds 68 stocks in its basket with double-digit allocation to the top two firms (read: ETF Winner and Loser from a Flattening Yield Curve).Zacks ETF Rank: #1 (Strong Buy)Average Daily Volume: 75.2 millionAUM: $23.13 billionExpense Ratio: 0.14%Top Sector: N/AYTD Returns: 6.2%SPDR S&P 500 ETF SPYThis fund tracks the S&P 500 index and holds 506 well-diversified stocks in its basket with each holding no more than 3.61% of the assets.Zacks ETF Rank: #2 (Buy)Average Daily Volume: 72.45 millionAUM: $239.9 billionExpense Ratio: 0.09%Top Sector: Information Technology (22.4%)YTD Returns: 9.9%iPath S&P 500 VIX Short-Term Futures ETN VXXThis ETN provides exposure to short-term equity market volatility by following the S&P 500 VIX Short-Term Futures Index Total Return with the help of the CBOE Volatility Index futures contracts (read: What Does Extremely Low VIX Say About ETF Investing?).Zacks ETF Rank: N/AAverage Daily Volume: 60.25 millionAUM: $1 billionExpense Ratio: 0.89%Top Sector: N/AYTD Returns: -51.7%VanEck Vectors Gold Miners ETF GDXThis product tracks the NYSE Arca Gold Miners Index, which measures the performance of companies involved in the gold mining industry. Holding 51 stocks, it is guilty of concentration on the top two firms that account for over 9% share each.Zacks ETF Rank: N/AAverage Daily Volume: 54.9 millionAUM: $8.7 billionExpense Ratio: 0.51%Top Sector: N/AYTD Returns: 7.2%iShares MSCI Emerging Markets ETF EEMThis fund targets emerging markets and follows the MSCI Emerging Markets Index. It holds 854 stocks in its basket with each accounting for less than 5% share (read: Why No Taper Tantrum for EM ETFs Now).Zacks ETF Rank: #3 (Hold)Average Daily Volume: $593.3 billionAUM: $32.4 billionExpense Ratio: 0.72%Top Sector: Information Technology (25.6%)YTD Returns: 19.7%ProShares Ultra VIX Short-Term Futures ETF UVXYThis product provides two times leveraged exposure to the S&P 500 VIX Short-Term Futures Index, which measures the returns of a portfolio of monthly VIX futures contracts with a weighted average of one month to expiration.Zacks ETF Rank: N/AAverage Daily Volume: 31.1 millionAUM: $355.5 millionExpense Ratio: 0.95%Top Sector: N/AYTD Returns: -79.3%United States Oil Fund USOThis is the most popular and liquid ETF in the oil commodity space and seeks to match the performance of the spot price of West Texas Intermediate (WTI or U.S. crude).Zacks ETF Rank: N/AAverage Daily Volume: 30.3 millionAUM: $3 billionExpense Ratio: 0.72%Top Sector: N/AYTD Returns: -21.5%PowerShares QQQ QQQThis product provides exposure to the 107 largest domestic and international companies excluding financial stocks by tracking the Nasdaq-100 Index. It is concentrated on the top firm at 11.5%.Zacks ETF Rank: #1Average Daily Volume: 29 millionAUM: $52.2 billionExpense Ratio: 0.20%Top Sector: Information Technology (57.6%)YTD Returns: 18.7%iShares Russell 2000 ETF IWMThis ETF targets the small cap segment by tracking the Russell 2000 Index, holding 2013 stocks with each holding less than 0.35% of the assets (read: Time to Buy Small Cap ETFs).Zacks ETF Rank: #3Average Daily Volume: 28.5 millionAUM: $38.7 billionExpense Ratio: 0.20%Top Sector: Financials (18%)YTD Returns: 5.6%iShares MSCI EAFE ETF EFAThis fund provides exposure to the stocks in Europe, Australia, Asia and the Far East by tracking the MSCI EAFE Index. It holds 934 securities in its basket with each holding less than 2% of assets.Zacks ETF Rank: #2Average Daily Volume: 20.3 millionAUM: $76.9 billionExpense Ratio: 0.33%Top Sector: Financials (20.9%)YTD Returns: 15.8%Want key ETF info delivered straight to your inbox?Zacks’ free Fund Newsletter will brief you on top news and analysis, as well as top-performing ETFs, each week. Get it free >>Want the latest recommendations from Zacks Investment Research? Today, you can download 7 Best Stocks for the Next 30 Days. Click to get this free report NASDAQ-100 SHRS (QQQ): ETF Research Reports SPDR-SP 500 TR (SPY): ETF Research Reports ISHARS-EMG MKT (EEM): ETF Research Reports ISHARS-R 2000 (IWM): ETF Research Reports US-OIL FUND LP (USO): ETF Research Reports SPDR-FINL SELS (XLF): ETF Research Reports PRO-ULT VIX STF (UVXY): ETF Research Reports IPATH-SP5 VX ST (VXX): ETF Research Reports ISHARS-EAFE (EFA): ETF Research Reports VANECK-GOLD MNR (GDX): ETF Research Reports To read this article on Zacks.com click here. Zacks Investment Research Want the latest recommendations from Zacks Investment Research? Today, you can download 7 Best Stocks for the Next 30 Days. Click to get this free report