The last time that the price of gas was under $1.00 in the United States was the week of March 15, 1999. At that time, the average price of gas per gallon was 97 cents.
Although there were several periods throughout the 1990s when gasoline averaged under one dollar (the longest of which was between December 1998 and March 1999), for most of the decade gas prices were over $1.00. The last decade in American history in which gas prices consistently averaged less than $1.00 was the 1970s. Between 1980 and 1981, gas prices rose to above $1.00 and have, for the most part, remained above $1.00 as of 2014.