Gas prices have slid to the lowest prices of the year as an estimated 84 million Americans prepare to take a road trip by car this holiday season.

The national average retail gasoline price on Monday is the cheapest it has been during 2012 — just shy of $3.25 a gallon, according to AAA and Oil Price Information Service.

The national average price has dropped every day this month and has fallen 16 percent since mid-September. It is now at the lowest average price since Dec. 28, 2011, and only 4 cents shy of the December 2011 low of $3.206 a gallon.

"I believe we will go lower than that," said OPIS analyst Tom Kloza. "It's typical to get weaker prices at the end of the year."