The Dept. of Energy tracks gasoline prices over history. The US Energy Information Administration has the prices for oil and gas going back decades. They also show the prices in real (inflation adjusted) terms.
Here is a graphic showing the monthly gasoline prices both nominal and real going all the way back to 1919. The inflation adjusted prices in red and the actual prices are in blue.
Note that these are annual averages so it doesn't reflect the daily or monthly highs and lows.
They also have the monthly prices going back to 1976.
|Source : EIA|
There you can see that the peak in both real and nominal terms was the summer of 2008. Back in '08 the price of gasoline hit $4.06 a gallon which is equivalent to about $4.10 in todays dollars. Note the grey bit on the far right is just 'forecast' of the future.
If you want to see more of the data then you can go to the EIA website. They have a gizmo there that lets you look at a chart of prices for specific dates. Plus they have a full Excel sheet with all the data and the charts that I've included above.
Gas pump photo by Candie_N