Have you ever wondered how billionaires continue to get RICHER, while the rest of the world is struggling?

I study billionaires for a living. To be more specific, I study how these investors generate such huge and consistent profits in the stock markets — year-in and year-out.

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In fact, global economic worries have deepened after a recent report pointed that U.S. producer prices declined for the first time this year and China’s consumer inflation fell to the lowest level in five years.

Moreover, the Organization of the Petroleum Exporting Countries (OPEC) seems to be least concerned in preventing the slide. There are speculations doing the rounds that Saudi Arabia and other members of the OPEC will abstain from production cuts to drain surplus.

In fact, the largest producers of OPEC are instead cutting prices to compete for market share.  Their strategy is to curb investments and further increase supply from U.S. shale or other avenues. Moreover, oil production from OPEC countries rose to its highest level since the summer of 2013 in September, led by higher supply from Iraq and Libya .

The price cut rather than the supply cut has further led to a panicky situation in the oil markets, pushing oil futures into a bear market.

Adding to the concerns, International Energy Agency in Paris predicts global oil demand to rise by 650,000 barrels a day this year – the slowest growth since 2009 due to slowing growth in key areas like China and Europe (read: 3 Foreign ETFs Rising Despite Market Volatility ).

Given the situation, investors might want to consider shorting oil. Though futures or short-stock are some of the possible ways for doing so, there are a host of short oil ETF options which may make more sense for many investors.

So, for investors seeking to make an inverse bet on oil, we have highlighted below four ETFs, any of which can be used to make a short play on oil.

However, investors should keep in mind that a short play in the futures market requires a strong appetite for risks.

ProShares UltraShort DJ-UBS Crude Oil ETF  (SCO )

SCO is the most popular option in the short oil ETF space having an asset base of $169.1 million. The fund tracks the Dow Jones-UBS Crude Oil Sub-Index to provide twice the inverse performance, on a daily basis of WTI crude oil.

Volumes are also great as roughly 1.3 million shares change hand daily. However, expenses are a bit steep at roughly 95 basis points annually.