Two exchange traded funds overseen by bond giant PIMCO account for more than half the assets held in all actively managed ETFs.

At the end of March, there was $12.9 billion in active ETFs listed in the U.S., according to AdvisorShares Investments. [Active ETFs are ‘New Distribution Channel’ for Money Managers]

The largest active fund by far was PIMCO Total Return ETF (NYSEArca: BOND), which held $4.6 billion at the end of the first quarter. The ETF managed by Bill Gross now stands at about $5.2 billion. [ETF Chart of the Day: PIMCO Total Return]

BOND, the ETF version of PIMCO Total Return Fund, has grown rapidly after launching in March 2012. Gross has said the ETF is designed to allow smaller investors to get access to PIMCO’s strategies. [PIMCO Readies Three More Bond ETFs]

PIMCO Enhanced Short Maturity ETF (NYSEArca: MINT) has also been a success, as an alternative to money market funds. [Short Duration ETFs vs. Money Funds]

Next page: Breaking down the active ETF business

Active ETFs are a tiny fraction of the overall U.S. ETF business, which controlled $1.47 trillion at the end of March, according to Morningstar.

“What you see is that the majority of ETFs are index-tracking funds,” said Deborah Fuhr, partner and co-founder of research firm ETFGI, in a recent Pensions & Investments report. “There aren’t a lot of active ETFs out there — less than 1% of all ETF assets are in actively managed ETFs. To be fair, PIMCO is one of the few big firms with success in active ETFs. Others who offer them don’t have the global recognition with a long track record in active funds.”

At the end of March, PIMCO’s seven actively managed ETFs accounted for 60.7% of the active ETF market.

WisdomTree Investments (NasdaqGM: WETF) was next with 13 active ETFs and 25.9% market share, followed by AdvisorShares with 18 funds and 5.6% share.

BlackRock, the largest ETF manager, recently launched some active funds. [iShares Enters the Actively Managed ETF Arena]