TransCanada Corp., the company behind the Keystone XL Pipeline, said it agreed to buy U.S. natural gas pipeline operator Columbia Pipeline Group Inc. for $10.2 billion. Including $2.8 billion in Columbia Pipeline's debt, the deal is valued at $13 billion.

TransCanada will offer $25.50 per share in cash for each Columbia Pipeline share, an 8.5% premium to the stock's March 17 close.

TransCanada said it would finance the deal by selling its U.S. Northeast merchant power assets and a minority interest in its Mexican natural gas pipeline business.

The company said it had also secured $10.3 billion of credit facilities.

Goldman Sachs & Co and Lazard advised Columbia Pipeline, while Sullivan & Cromwell LLP and Bennett Jones LLP were its legal advisers.

Wells Fargo Securities LLC was TransCanada's financial adviser and Mayer Brown LLP, Blake, Cassels & Graydon LLP and Osler, Hoskin & Harcourt LLP were its legal advisers.