One of the most profitable activities in ETFs that past year has been buying funds that bet against market volatility as the VIX drops to the lowest levels since the financial crisis.

For example, VelocityShares Daily Inverse VIX Short Term ETN (NYSEArca: XIV) rallied 155% in 2012 and is up and additional 21% year to date, according to Morningstar. ProShares Short VIX Short-Term Futures ETF (NYSEArca: SVXY) has delivered similar eye-popping returns. [Inverse VIX ETFs Rise 170% as Volatility Hits Five-Year Low]

For comparison, SPDR S&P 500 ETF (NYSEArca: SPY) posted a total return of 16% last year and is up nearly 7% thus far in 2013.

XIV and SVXY are designed to move in the opposite direction of futures contracts based on the CBOE Volatility Index, or VIX, which is known as Wall Street’s fear index. It should be noted that inverse and leveraged products are designed as trading vehicles rather than buy-and-hold investments, so take their long-term performance with a grain of salt.

Technical analyst Chris Kimble at Kimble Charting Solutions notes that since June of last year, XIV has gained 120 percentage points more than the S&P 500 fund.

But how much longer can the good times last for these anti-VIX products?

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