TransCanada had a nice little party last weekend.

The company has been battling for years to win the State Department’s blessing to build the Keystone XL pipeline over the Canadian border to help export tar-sands oil to American refineries. Meanwhile, it has been building the southern leg of that same pipeline from Oklahoma to Texas.

On Saturday, the company started filling that southern leg with the sticky, polluting, climate-changing fuel that it will carry cross-country to the Texan refineries — crude oil.