Best I've ever got on a long trip from my VF1 3.6l auto is 6.8l/100km (using 91 octane fuel), which would give me a range of about 955km (leaving 5 litres in the tank for safety). This was on a mixture of freeways and rural roads, doing 100 - 110 km/h (plus the occasional squirt for overtaking). The VF is the only car I've ever had which can get me from Adelaide to Melbourne (about 730km) without refuelling, in complete comfort on a hot day with the air conditioning on, and still have 1/4 tank remaining at journey's end. I find that quite remarkable for a large, heavy car. Vale el Commodore!