If you need to be conscious of gas consumption for either environmental or wallet reasons, your best bet is to exercise good driving behaviors. I don't mean drive like grandma but, racing from red light to red light, slamming in brakes etc need to be weeded out. I find the G gives me the best mileage between 120 and 130 km/hr (whatever that is in miles). FWIW, my IS250 gets best mileage at 98 km/hr (exactly 60miles/hr). Seems the smaller displacement 2.5L in the IS does not like to work hard.

 

"Another reminder, if there is a gasoline truck pumping into the storage tanks when you stop to buy gas, DO NOT fill up; most likely the gasoline is being stirred up as the gas is being delivered, and you might pick up some of the dirt that normally settles on the bottom"

That is one advice my friend always told me if you see the truck do not gas there.