I drive on the motorway a lot (150 sri vectra) at 70 i get in the 30's, but went to newquay a few weeks back, did 503 miles in total, could have got home on one tank,b ut didnt risk and stuck some more in, but it avaeraged 49 mpg !! I put it down to their type of roads, they are all national limit roads where my car literally ticks over whilst driving them !! lol