Whether TransCanada will build the Keystone XL after overcoming its last major regulatory hurdle Monday has become an open question after nine years of planning because the project may no longer be economically viable.

Oil prices surpassed $130 a barrel when TransCanada first sought a cross-border permit for the pipeline in 2008. But oil prices have been trading for less than half that for the last several years, as an oil glut prompted prices to plunge. Crude oil currently is trading at about $60 a barrel on world markets.