Oil shipments on Wednesday began to flow through Keystone XL's southern leg.
TransCanada announced the start of oil deliveries to Gulf Coast refineries on Wednesday morning. The shipments run from Cushing, Okla. to Nederland, Texas.
Green groups like the Sierra Club blasted the administration for failing to adequately review the pipeline.
“Today’s announcement is a painful example of President Obama’s all of the above energy plan at work: polluted air and water, carbon pollution, and the ever present threat of poisoned drinking water for millions of Texas and Oklahoma families," Sierra Club Executive Director Michael Brune said in a statement.
"The Sierra Club will fight hard to protect the families who are now at risk, and turn the Obama administration’s shortsighted dirty energy policy around,” added Brune, who is normally a fan of Obama's climate agenda.
The environmental advocacy group 350.org's Bill McKibben, also pointed the finger at Obama for falling out of line with his promises to battle climate change.
"Expediting KXL south was not the mark of a president who really 'gets' climate change," McKibben said in a statement on Wednesday.
Officials with TransCanada, the company responsible for building the pipeline, celebrated the opening of the southern leg while touting their safety standards.
TransCanada's CEO called Keystone XL “the safest oil pipeline built in America to date” during a Wednesday conference call.
CEO Russ Girling said he expects the success of the southern leg will prove the case for its more controversial Alberta-to-the Gulf Coast northern leg.
The administration still faces a decision on approving Keystone's northern leg, which would carry crude from the oil sands in Alberta to Gulf Coast refineries.
The northern leg require approval from the president because it crosses over the U.S. border with Canada.
This story was updated at 2:45 p.m.