Gas prices at pumps across the nation have fallen for 43 of the past 44 days, dropping 22 cents during this span, according to the latest data from AAA. The national average price for regular unleaded gasoline sits at $2.21 per gallon, which is the lowest mark since April and the lowest price for this date since 2004. Today’s price is five cents less than one week ago, 15 cents less than one month ago and 56 cents less than the same date last year.

With abundant fuel supplies across the nation and declining crude oil costs, gas prices dropped in 47 states over the past week, led by double-digit drops in several Midwestern states. Gas prices dropped in 48 states during the previous month with prices down by at least 25 cents per gallon in Illinois, Ohio, Kentucky, Indiana and Michigan.

Prices are substantially lower than one year ago in every state, headlined by California, where prices are more than a dollar cheaper than this time last year.

Today’s most common price in the country is $1.999 per gallon, and more than one-third of gas stations nationwide are selling gasoline for $2 per gallon or less. This is substantially higher than the seven percent of stations at or below this threshold a month ago and the fractions of percent that broke this mark a year ago.

Gas prices are likely to remain low for the remainder of the summer compared to recent years. U.S. crude oil supplies are at their highest level for this time of year in 86 years, although domestic oil production has ticked lower each of the past nine months. While oil production has slowed slightly, fuel production has continued to rise.

This is supported by data from the American Petroleum Institute, which last week reported fuel deliveries for June were three percent higher than 2015 and the highest number in nine years. Overall, domestic deliveries are 1.7 percent higher during the first half of 2016 than the same period last year, which is in line with AAA reports of travelers taking advantage of lower gas prices and hitting the roads in record numbers this year.

Despite the lowest seasonal prices in 12 years, it’s important to note the possibility that unexpected events could trigger higher prices later this summer. For example, crude oil costs could rise due to disruptions in supply, stronger than expected economic growth or geopolitical tensions overseas. In addition, regional prices could increase due to refinery problems, production cuts, stronger than anticipated demand, or hurricanes that impact distribution and production.