MasterCard reported that in July, gasoline demand posted its lowest monthly average since the company has been keeping records, as consumers faced steeper costs at the pump and worried about the economy.

Separate data compiled by the US government showed gasoline demand in July was at its weakest in eight years and was slower than it was after the financial crisis.

Gasoline demand in the US has been weak since prices shot up to $3.50 a gallon in March.

MasterCard said four-week US average demand in July hovered just above 65 million barrels, the lowest since the company started releasing weekly gasoline sales data in 2005, based on its own credit card data and estimates for cash and check purchases.

Over the latest four weeks leading up to Aug. 5, average US gasoline consumption fell 2.2 percent from year-earlier levels, marking the 20th straight decline for the four-week average.

“The overlying economic uncertainty and the higher prices are driving the weakness in demand,” said gasoline analyst John Gamel with MasterCard.

He said record temperatures all over the country, along with improved fuel efficiency of the US vehicle fleet, may also have helped cut demand.

The last two weeks of July were weaker than a year ago, Gamel added.

MasterCard said high pump prices restrained demand. A gallon of gasoline went for $3.70 on average last week, unchanged from a week ago but about 34.5 percent higher than 2010.

Weekly data from the US Energy Information Administration (EIA) last week showed US four-week average gasoline demand in July averaged 9.2 million barrels-a-day, the lowest for the month since 2003.

On Monday, the average price of gasoline in the US was at $3.65 a gallon, 3.0 cents cheaper than a week ago, EIA said.

Gasoline futures on the New York Mercantile Exchange (NYMEX) have been on a steady decline since late July and have fallen about 48 cents over the last two weeks, but this has not yet translated into cheaper prices at service stations.

“There is a layered effect. It takes one to two weeks for a change in the commodities market to show up at the pump,” Gamel said.

“Even if prices fell, consumers don’t react the same week.”

Average gasoline demand last week, which includes the last two days of July, fell 3.3 percent and declined 1.8 percent versus the previous week, MasterCard’s report said.