(Portland, OR) -- Gas prices in Oregon are up four cents a gallon over the last week to four-66. Triple-A reports the national average is also up four cents to three-82. Medford has the highest prices in the state at four-77 while Pendleton has the least expensive gas at four-49 a gallon. The increase is mainly due to high crude oil prices and heat in the southern U.S. that's reducing production at refineries. Oregon's move to some self-service pumps is not expected to affect prices, because it's the same for full-serve and self-serve. Diesel in Oregon increased 11 cents to four-61 a gallon.