HOUSTON (February 21, 2013)-- Retail gasoline prices across Texas jumped 21 cents in the past week as U.S. refineries prepare to switch to more expensive summer-blend gas, AAA-Texas said Thursday.

AAA says the average price per gallon reached $3.64 in Texas while the nationwide average price of gasoline rose 15 cents this week to hit $3.78 per gallon.

The association says Dallas has the most expensive gasoline statewide at $3.71 per gallon.

The cheapest gasoline was in Amarillo at $3.52 per gallon.

AAA says the updated gasoline blend is expected to reach markets in a couple of weeks but until then prices at the pump could continue on the upswing.