Mazout!  Or fuel oil. It's made up of Carbon, Hydrogen, Sulfer, Nitrogen and a little bit of Oxygen.  The hubs and I have learned that this is something you never want to run out of!  Many Americans refuse to rent a house with Mazout.  Mainly because they feel that it is expensive.  Really, in the grand scheme of things, mazout is not expensive.  It's just that when you buy it, you buy it in bulk, so it's not uncommon to spend 2000 US Dollars for a delivery.  The great thing is that you have very very low electricity bills!
Yesterday when we checked our tank, we had approx 600 liters.  In a couple months, we will request a new delivery.  The Mazout truck will come to the house and a hose will run from the truck to our tank that sits beneath the garage.  The truck will pump a pre determined amount of mazout into the tank and the nice guy that works for the company will hand us a bill.  It's amazing how quick a family of Floridians can freeze in a house when the tank runs low!  We won't talk about how cold the showers get!

Very similar to checking the oil in your car!

It's very important to not run out of Mazout before you see this truck at your house!