US pressure pumper Liberty Oilfield Services is planning an initial public offering of shares to help it increase the size of its fracturing fleet by more than 50% by the end of the year.

Denver-based Liberty hopes to raise about $50 million through a share offer on the New York Stock Exchange, which is will use to add six fracturing spreads to its existing fleet of 11 spreads totalling 440,000 horsepower, according to a filing with the US Securities & Exchange Commission (SEC).

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