The average price of a gallon of gasoline in the United States gained 8 cents in the past three weeks, according to a survey released on Sunday.

Regular-grade gasoline climbed to around $2.10 a gallon in the Friday survey, from $2.02 a gallon on March 18, survey publisher Trilby Lundberg said in an interview.

The latest price was the highest since Dec. 4, Lundberg said in an interview. Gasoline prices have risen 33 cents since Feb. 19, she said.

The recent rise in gasoline prices has little to do with U.S crude oil prices, Lundberg said.

U.S. crude futures CLc1 inched up to $39.72 cents on Friday from $39.44 on March 18.

“Even if crude oil prices keep meandering with no decisive climb, we may still see pump prices rise short-term,” Lundberg said.

The rise in gasoline prices is partly because of a seasonal increase in demand as more people are on the road as the weather improves and the days are longer. The improvement in the economy has also led to more auto sales, Lundberg said.

Many U.S. refiners are also still preparing summer-grade gasoline, which costs more to make because it has a lower vapor pressure to prevent smog, she said. The deadline in most of the country to make summer-grade gasoline is May 1.

In the Lundberg panel of about 2,500 gas stations in large cities in 48 states, the lowest average retail price for gasoline was in Tulsa, Oklahoma, at $1.67 per gallon, and the highest was in Los Angeles at $2.80 a gallon.