

[ALSO: Experts: Rail a Feasible Alternative for Keystone XL]

Paul Sullivan, a professor of economics at National Defense University and an adjunct at Georgetown University, also voiced some skepticism about the company's numbers.

"This seems to not take into account the alternative sources making this pipeline less important," he says. Pointing to CERI numbers that TransCanada shared in 2012, he adds, "I find it odd that they came up with just one number instead of a range given that this pipeline will be working for many decades to come. A number from 100,000 to 400,000 may not be too far off, but that would be determined by scenarios," projections ranging from how development of renewable-energy might influence oil demand, to how geopolitical situations in Russia, or the Mideast might affect prices.

Nevertheless, this "first impression" that Keystone XL will fuel major job growth -- perhaps on the scale of nearly a half-million jobs -- has apparently become a lasting one, says Katherine Krimmel, an assistant professor of political science at Boston University.