J.P. Morgan analyst Jamie Baker said that as of Wednesday morning, no other major airlines had matched United's move.
United's increase ranged from $4 to $10 per round trip depending on distance. Baker says it's the 12th attempt this year by airlines to raise fares, but only four have succeeded.
FareCompare.com CEO Rick Seaney says the fare increase doesn't affect sale prices for off-peak winter travel that were introduced Tuesday by Southwest Airlines and widely matched by others.
United didn't immediately return messages for comment.
Airlines usually roll back increases if key competitors decline to match them because many consumers will switch airlines to save even a few dollars.