That means if your heating oil tank gauge reads ½, you don’t have 140 gallons in your tank. You have about 110 gallons. If the float is at the bottom of the gauge or is not visible, your heating oil tank is almost empty or actually empty. Call Resnick Energy right away to schedule an emergency heating oil delivery. We offer 24/7 emergency heating oil delivery, 365 days a year. If your oil tank gauge has a thin indicator disc such as the red disc shown in the oil tank gauge above, read the oil level at the center of the disc. It's not that precise anyhow. If your oil tank gauge has a thick indicator disc like the more-recent Scully oil tank gauge shown below, our experiments to date (January 2020) suggest you should read the oil level at the top of the yellow disc. broken or if your tank is out of fuel. By reading your own oil tank gauge, you can save money and brush up on your maintenance skills. 1. Locate the oil tank gauge in or outside of your home. The gauges are usually located on top of the oil tank and look like a rounded cylinder. 2. Look for the floating assembly inside the gauge.