Alibaba IPO ranks as world's biggest after additional shares sold

* IPO breaks global record, surpassing Agricultural Bank of China

* Underwriters to earn $300.4 mln in fees, 1.2 pct of IPO

* Company sells 26.1 mln additional shares, Yahoo 18.3 mln

* Jack Ma, Joe Tsai also sell additional shares (Adds Breakingviews link)

By Elzio Barreto

HONG KONG, Sept 22 (Reuters) - Alibaba's initial public offering now ranks as the world's biggest at $25 billion, netting underwriters of the sale a more than $300 million windfall after the e-commerce giant and some shareholders parted with additional shares.

The fees are equivalent to 1.2 percent of the total deal, with Alibaba paying $121.8 million in commissions. Selling shareholders are set to pay another $178.6 million, according to a filing with the U.S. Securities and Exchange Commission on Monday.

Overwhelming demand saw the IPO initially raise $21.8 billion, and then sent Alibaba Group Holding Ltd's stock surging 38 percent in its debut on Friday. That prompted underwriters to exercise an option to sell an additional 48 million shares, a source with direct knowledge of the deal said.

That means the IPO has surpassed a previous global record set by Agricultural Bank of China Ltd in 2010, when the lender raised $22.1 billion.

According to its prospectus, Alibaba had agreed to sell 26.1 million additional shares under the option, and Yahoo Inc an additional 18.3 million, netting the two companies an extra $1.8 billion and $1.2 billion respectively.

Alibaba's Jack Ma had agreed under the same option to sell an extra 2.7 million shares and company co-founder Joe Tsai agreed to 902,782 additional shares.

The source declined to be identified as the details of the additional sale have yet to be made official.

Alibaba declined to comment.

Citigroup Inc, Credit Suisse Group AG, Deutsche Bank, Goldman Sachs Group Inc, JPMorgan Chase & Co and Morgan Stanley acted as joint bookrunners of the IPO.

Rothschild was hired as Alibaba's independent financial advisor on the deal.

(Reporting by Elzio Barreto; Editing by Denny Thomas, Edwina Gibbs and Clara Ferreira Marques)