( CNN ) -- After nearing the all-time record , gas prices in the United States are sliding downward , with another drop possible in the next few days , according to a survey published Sunday . The Lundberg Survey found the average price of a gallon of self-serve regular gasoline nationwide was $ 3.91 as of Friday , publisher Trilby Lundberg said . The price represents a drop of just over 9 cents from May 6 , when prices hit the $ 4 mark . The all-time high for U.S. gas prices was $ 4.11 on July 11 , 2008 , she said . The drop `` comes from the crude oil price slump earlier this month , '' Lundberg said , `` and it looks like there 's perhaps another dime drop at the pump in the next few days . '' However , whether the drop is more or less than a dime depends on several factors , including what crude oil prices do next and whether flooding in the Southeast , which has caused transport delays , does not worsen , she said . Asked whether crude oil prices may rise again , Lundberg said , `` It certainly is possible at any time . '' However , the recent high prices have contributed to a dampening of world demand , she said , and demand at the pump in the United States is down `` with a double whammy '' -- unemployment and underemployment , as well as the Southeast flooding . The Friday price is about $ 1.08 higher than the price a year ago -- $ 2.83 on May 21 , 2010 . The city with the highest average price in the latest survey was Chicago , at $ 4.38 per gallon , Lundberg said . The lowest was Jackson , Mississippi , at $ 3.60 . Different tax levels in different states are a major factor in bringing about diverse prices . Here are some other average prices in a panel of large cities : . -- Salt Lake City $ 3.67 . -- St. Louis $ 3.74 . -- Houston $ 3.79 . -- Atlanta $ 3.91 . -- Boston $ 3.98 . -- San Francisco Bay area $ 4.17 .
The average selling price is $ 3.91 per unit . That 's a drop of just over two percent from May 6 . The all - time high is $ 4.11 in May 2008 .