Eugene Oregon to Mill Valley, CA. 529 miles in one tank. We've done it more than once in our Volvo 850 wagon 5 speed. We usually average around 30-33mpg depending on how much AC we use. I stick to the speed limit.
Average MPG.
Miles to empty at average MPG.
map
http://maps.google.com/maps?f=d&sadd...63&ie=UTF8&z=6
600 miles to the tank is conceivable but I don't think I want to let the fuel get that low. I love my old 960. I passed it on to my parents. But the 850 is definitely a step above in both fuel economy and functionality. The aerodynamic undertray also helps.