Shares of Kansas City Southern (KSU) jumped after the Wall Street Journal reported that Blackstone Group (BX) and Global Infrastructure Partners are considering a takeover bid for the railroad operator that could be worth more than $21 billion.

The private equity firms are speaking to banks including Citigroup (C) about financing, Cara Lombardo and Miriam Gottfried report, citing people familiar with the matter. However, the roughly $15 billion equity check that could be required for a deal "would pose significant hurdles" for Blackstone and GIP, they add. The bid being discussed would likely include about $6.5 billion worth of debt financing, sources told the Journal.

Shares of Kansas City Southern rose 14% to $178.85 following the report.