The U.S. State Department requested public opinion on a draft assessment of the planned cross-border pipeline.
Critics of the project say Canadian crude oil, the type designated for Keystone XL, may be more corrosive and therefore more likely to cause a pipeline spill.
A so-called tar sands oil spill in Michigan in 2010 was the costliest incident of its kind. Exxon Mobil is working to clean up a similar spill in Arkansas, though that spill is far less severe than Michigan's.
Brigham McCown, former director of the federal Pipeline and Hazardous Materials Safety Administration, brushed off some of the safety concerns.
"I do want to point out that pipelines are the safest means to transport energy products in this country," he was quoted by the Lincoln (Neb.) Journal Star as saying.
The newspaper said the State Department took comments from supporters and detractors in a lengthy meeting Thursday.
TransCanada Vice President Corey Goulet told the Journal Star he didn't think the Arkansas spill would factor into the decision on Keystone XL.
"I don't like to make comparisons because a pipeline properly maintained can last indefinitely," he said.
Exxon's pipeline, Pegasus, was installed in the 1940s.
U.S. Assistant Secretary of State Kerri-Ann Jones said the government would consider things like Keystone XL consumers when considering the thousands of comments submitted on the draft report. No indication was given as to when a final decision was expected.
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