This is the highest price recorded in March, according to data going back to 1990.
Some consumers have been paying more than $4 a gallon for weeks. This week's average price for regular gas was up 27 cents from a year ago, and up 7 cents from last week.
GasBuddy, which provides local prices online and through its mobile app, shows an increase of 5 cents per gallon on average from last week.
Patrick DeHaan, senior petroleum analyst with GasBuddy, said every community in California is now above $4 a gallon. Gas prices in other metropolitan areas are rising as well. Chicago is now above $4, a 45 cent a gallon rise in a month, DeHaan said.
DeHaan said he was not shocked at the Energy Department's weekly average because "the fear of a production or supply issue is certainly driving additional speculation in the market."
Gas prices are still "playing a game of catch-up" to oil and wholesale gas prices, which have risen sharply in the past few weeks, DeHaan said. Oil prices are up more than 2 percent in the past year.
Light, sweet crude oil futures for April ended the week Friday at $106.70, according to the Chicago Mercantile Exchange Group, down from its highest settled price last week of $108.84 Thursday.
Related to speculation in the market, geopolitical concerns have helped to drive up oil prices as the showdown over Iran continues. The head of the United Nation's nuclear agency, Yukiya Amano, said early today that he has "serious concerns" about new activity related to nuclear weapons development. Fear is growing that Israel's air force might strike Iran to try to destroy its nuclear facilities.
Iranian officials have warned for months that they would close a key oil passageway, the Strait of Hormuz, if their country is threatened. The strait connects to the Persian Gulf and sees handles about a fifth of the world's oil in transit.
If Iran becomes more hostile and causes a supply disruption, oil prices could soar to all-time highs and approach $175 to $200 a barrel, DeHaan said.
Iran holds the world's fourth-largest proven oil reserves, and the world's second-largest natural gas reserves, according to the Energy Information Administration.
GasBuddy has forecasted 2012 to be the "worst" year for gas prices.
The real annual average for a gallon of regular gas last year hit $3.56, up from $2.90 in 2010, according to the EIA. From its data that begins in 1919, the previous record high was in 1981, at $3.45.
Gasoline prices had the longest stretch of days of $4 or more in 2008, but the yearly average was $3.24, according to GasBuddy's data, which goes back to 2000.
Gas prices slid in October to December 2008 to less than $2 a gallon nationally.
ABC News' Zunaira Zaki contributed to this report.