Thanks to everyone who answered. My 9 miles isn't unprecedented!
(The problem is that in the highlands, villages are few, villages with filling stations fewer, and villages with a fuel station open on a Sunday are rare birds indeed. I usually get about 120 miles from a tank at the speeds I choose to travel at - 60 to 70 mph. But with often 50 miles between petrol stations one has to be VERY confident to sail past one after only 70 miles travelled. And stopping every 70 miles makes for long journeys. Hence the acquisition of a 5 gallon tank.)
(The problem is that in the highlands, villages are few, villages with filling stations fewer, and villages with a fuel station open on a Sunday are rare birds indeed. I usually get about 120 miles from a tank at the speeds I choose to travel at - 60 to 70 mph. But with often 50 miles between petrol stations one has to be VERY confident to sail past one after only 70 miles travelled. And stopping every 70 miles makes for long journeys. Hence the acquisition of a 5 gallon tank.)