Nice graph showing gas prices from 1918 (yes, that's right) in nominal terms and adjusted for inflation. Quite interesting!!

Here are 2 measures of gasoline prices dating from 1918. The black line is in nominal prices--just the price of a gallon of gas in a given years price (not adjusted for inflation).

The red line is adjusted for inflation over time.  It is measured in 2011 prices. The year 1981 is noted on the graph. The nominal price in that year was $1.35/gal. In 2011 dollars that would be equivalent to $3.31/gal.  In other words, what cost you $1.35 in 1981 would have cost you $3.31 in 2011. 

Source: Inflationdata