25 Most Liquid U.S. ETFs - Source: http://etfdb.com/compare/volume/

Symbol	Name	Avg Volume	AUM
SPY	SPDR S&P 500	264,139,844	$92,765.3 M
XLF	Financial Select Sector SPDR	114,593,563	$5,020.5 M
IWM	Russell 2000 Index Fund	76,595,117	$14,000.7 M
EEM	MSCI Emerging Index Fund	73,868,984	$33,643.3 M
QQQ	QQQ	70,725,813	$25,296.3 M
SDS	UltraShort S&P500	42,540,879	$2,093.6 M
TZA	Daily Small Cap Bear 3X Shares	30,891,717	$692.2 M
TNA	Daily Small Cap Bull 3X Shares	30,128,217	$1,080.4 M
VWO	Emerging Markets ETF	27,954,180	$44,532.9 M
FXI	FTSE China 25 Index Fund	26,524,771	$6,749.0 M
EFA	MSCI EAFE Index Fund	26,484,469	$36,586.9 M
VXX	S&P 500 VIX Short-Term Futures ETN	26,445,979	$894.6 M
SLV	Silver Trust	25,556,166	$9,925.9 M
FAZ	Daily Financial Bear 3X Shares	22,810,010	$859.0 M
XLE	Energy Select Sector SPDR	22,784,221	$7,595.9 M
XLI	Industrial Select Sector SPDR	21,608,334	$3,009.3 M
SSO	Ultra S&P500	20,594,908	$1,559.9 M
EWJ	MSCI Japan Index Fund	19,539,520	$5,919.6 M
EWZ	MSCI Brazil Index Fund	18,067,178	$10,276.4 M
SPXU	UltraPro Short S&P500	17,274,531	$600.8 M
GLD	SPDR Gold Trust	15,999,109	$72,389.7 M
FAS	Daily Financial Bull 3X Shares	15,028,640	$1,504.0 M
XLB	Materials Select Sector SPDR	14,921,679	$1,751.7 M
GDX	Market Vectors TR Gold Miners	14,265,567	$7,909.5 M
USO	United States Oil Fund	12,420,987	$1,602.9 M