Oil prices and the fuel efficiency of new cars
In the 1990's, the average fuel consumption of new cars sold in the U.S. stayed stable at about 8–8.5 liters per 100 km. During that period the price of Brent oil was relatively low and stable. Then, around year 2000 it started a long upward trend. Almost simultaneously, the fuel efficiency of new cars in the U.S. and the UK improved. By 2014, the average new car sold in the U.S. consumed about 7 liters per 100 km. In the UK, fuel consumption dropped even more significantly to 6 liters per 100 km. New data that will become available in the future will show if the trend of declining fuel consumption was reverses after 2014 when oil prices collapsed.
For our U.S. audience, here is the same chart but in miles per gallon.
The data for these charts are provided by the Departments of Transportation of the two countries.