ProShares has officially joined the exchange-traded funds 3x party.

The leader in leveraged ETFs launched Thursday a pair of portfolios that will put it into a different sort of niche market. Each of the new ETFs will aim at providing 300% exposure -- both inverse as well as leveraged -- to the S&P 500 index.

The new ETFs are the: ProShares UltraPro S&P 500 (NYSE Arca: UPRO) and ProShares UltraPro Short S&P 500 (NYSE Arca: SPXU).

ProShares has surged to become one of the most popular ETF families offering straight one-to-one leverage and inverse exposure to popular indexes. But in recent years it has also expaned into sponsoring ETFs that've upped the ante in leverage to 200% of various benchmarks.

In those so-called 2x funds, ProShares seek to match the daily returns of their underlying indexes with 200% leverage or inverse positions.

It's a field that has become increasingly popular and includes Rydex. But late last year, a relative newcomer joined the leveraged crowd with ETFs that provide even greater exposure 300% both in terms of taking short positions with indexes as well as others that go long.

The debut of Direxion's 3x family in November 2008 came just as the market's volatility was soaring. As a result, investors—by and large traders and institutions—have jumped on the bandwagon of the firm's hyper-juiced funds. (See related story here.)

Since then, Direxion has rapidly climbed to No. 10 in terms of asset size among U.S. ETF players. (See related article with the latest industry data here.)

The launches follow a filing earlier this week of each fund's prospectus with the Securities and Exchange Commission. (Complete details about each fund, along with a link to the filing, can be found here.)

As noted in the previous story, the new 3x ETFs will be the first to provide such leverage to the S&P 500. But it also will put ProShares, which had $26.2 billion in assets through May, into a quickly growing and popular area of the leveraged ETF market.

As markets recover in coming years, will 3x leverage still find the groundswell of support it seems to currently hold? ProShares is obviously betting traders will continue to see these funds as important tools in their warchests as market cycles zig and zag.