266 gallons should see you through the end of this winter, and into the start of the next, even if you use some to supplement hot water, like here... the furnace dumps hot water into the hot water heater so it doesn't use as much electricity, which costs a lot more than fuel oil, this year anyway... glad you checked, if you're worried, they have a minimum usually... but you don't have to fill it. I'm outside the village, so I have to get 150 gallons min, in the village, it's 100... I get nervous when it hits a quarter tank, sometimes I don't get their "minimum" but it's not like they suck it back out... lol