Gauges are meant to give you an idea of how much oil is in your tank.  That is why it is best to always order at 1/4.

• The most common sized tanks are 275 and 330 gallons
• A tank cannot be filled to the top,  Oil expands and contracts with temperature. 
• A whistle is about 6 inches down from the top of the tank
• A whistle alerts the driver when to shut down the delivery
• A 275 tank will hold about 250 gallons ,   A 330 tank will hold about 300 gallons
• Not all gauges are the same
• Yellow gauges you go by the top of the yellow part

Just a hair above 1/4

Just about 3/8 ths

This is 1/8th with this sort of gauge.
​Go by top of yellow gauge

5/8ths of a tank with this gauge.
Go by top of yellow gauge.

This is 1/8th, Approximately
​ 33 gallons left in tank

Best time to order when the top of the yellow hits that red line.

This is at half a tank.

Older gauge reading 1/8th