US gas prices have fallen sharply since June.JOSEPH PREZIOSO/Getty Images US gas prices are on the rise again, stoking concerns that it could fuel inflation. The average gallon of gas traded at $3.89, its highest level since October 2022. Economist Mohamed El-Erian said this was why people were worried about an "inflation smile." US gas prices are on the rise again, threatening to worsen an inflation problem the Federal Reserve has worked hard to fight over the past year.