HOUSTON (AP) - Retail gasoline prices across Texas have jumped 21 cents in the past week as U.S. refineries prepare to switch to more expensive summer-blend gas.

AAA Texas on Thursday reported the average price per gallon reached $3.64. 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 found 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.

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