Investors pulled a net $150 billion from Pacific Investment Management Co.'s mutual funds in 2014, the largest annual exodus ever experienced by a mutual fund firm, according to preliminary figures Tuesday from fund research firm Morningstar Inc.

In the final month of the year clients withdrew $26.7 billion, including about $18 billion from Pimco's flagship Total Return fund. That figure differs slightly from the $19.4 billion in December withdrawals from Total Return that Pimco disclosed Friday because of the way assets are counted.

Star manager Bill Gross ran Total Return before leaving abruptly in late September for rival investment firm Janus Capital Group Inc., and withdrawals at Pimco jumped following his exit. The Total Return fund accounted for $103 billion of the $150 billion in outflows for the year, according to Morningstar.

Analysts have said that Newport Beach, Calif.-based Pimco should be able to withstand the outflow of money. The firm had $1.87 trillion in assets under management at the end of September, the latest data available, and Morningstar has said the firm could handle up to $350 billion in investor outflows over the next two years.

A Pimco spokesman didn't immediately return a request for comment.

The last time a fund company saw withdrawals of this size was in 2011, when investors pulled about $82 billion from Los Angeles-based American Funds amid poor performance, according to Morningstar.

Write to Kirsten Grind at kirsten.grind@wsj.com

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