(Portland, OR) -- Gas prices are up nationwide, but in Oregon prices are trending down. Triple-A reports the national average increased three cents last week to three-84 a gallon, because of refinery issues in Midwestern states. That's not the case in Oregon where prices declined three cents to four-71 a gallon. This week, refineries will begin the switch to less expensive winter blends of fuel and that should put downward pressure on prices, but crude oil prices are higher and that could slow the declines. Diesel in Oregon continues to soar, up six cents to five-20 a gallon.