(Reuters) - Ocwen Financial Corp (>> Ocwen Financial Corp) said it would buy mortgage servicing rights and related advances from OneWest Bank for $2.53 billion, the latest in a string of acquisitions that have fuelled the company's explosive growth and nearly tripled its shares over the past year.

Under the deal, Ocwen will purchase about $78 billion in unpaid principal balances of mortgage servicing rights (MSRs) through a combination of cash and available credit.

The total purchase price includes $446 million in respect of the MSRs and about $2.1 billion for the servicing advances, Ocwen said in a regulatory filing.

Atlanta-based Ocwen has been picking up companies that collect payments on subprime mortgages - known as servicers - or the underlying service rights, as banks and private equity firms look to shed them because of new regulations and capital requirements.

It bought mortgage lender Homeward Residential Holdings from Wilbur Ross' private equity firm for $750 million last October. Ocwen also bought the majority of Ally Bank's MSR portfolio for $585 million earlier this year.

The fast growth of mortgage servicers, including Ocwen and peers such as Nationstar Mortgage Holdings Inc (>> Nationstar Mortgage Holdings Inc) and Walter Investment Management Corp (>> Walter Investment Management Corp), have drawn scrutiny from regulators, who have been more watchful of the home mortgage business after the housing bust in 2007-2009.

Ocwen's portfolio more than doubled from the fourth quarter to the first quarter, and the company is now servicing more mortgages, as measured in dollars, than banks such as Citigroup Inc (>> Citigroup Inc) and U.S. Bancorp (>> U.S. Bancorp).

The OneWest deal is expected to close in stages during the second half of the year, Ocwen said.

Pasadena, California-based OneWest is a federal savings bank with 75 retail branches and over $25 billion in assets.

Both companies have agreed to set a termination fee of $50 million in case the deal does not go through.

Ocwen shares closed up 4 percent at $45.74 on the New York Stock Exchange on Thursday. They were up about 3 percent in extended trading.

(Reporting by Aman Shah in Bangalore; Editing by Maju Samuel)