ALEXANDRIA, Va. – Just as quickly as consumer optimism surged in July, it plummeted in August, despite gas prices falling by more than 15 cents over the past month.

Fewer than 4 in 10 consumers (39%) now say that they are optimistic about the economy, a sharp decline from 46% optimism the month prior. Consumers age 50 or older were least optimistic, with barely one in three (35%) expressing optimism. The 7-point drop overall in optimism was the largest recorded since January 2013 when NACS introduced its monthly NACS Consumer Fuels Survey to examine how gas prices affect consumer sentiment.

“The dramatic swings in consumer optimism over the past two months clearly show that sentiment remains fragile,” said Jeff Lenard, NACS vice president of strategic industry initiatives. “A rise or fall in everyday expenses — like gas prices — is usually an accurate predictor of sentiment unless something significant occurs, and this month it is clear that the recent sharp drop in stock prices — and concerns over world events — shook up consumers.”

While other economic concerns today weigh more heavily on consumers, gas prices remain top of mind. Nearly four in 10 consumers (39%) say that gas prices have a great impact on their feelings about the economic, a slight decrease from 41% the month prior.

If there is any good news in the findings, it’s that consumers don’t expect things to necessarily get worse — at least at the gas pump. Consumers tend to be naturally pessimistic about gas prices but less than half (47%) expect prices to be higher next month, a low for 2014 and a sharp drop from July (64%).