In an e-mail making its way around the Internet, a petroleum industry employee is trying to make gas consumers aware of ways to save money while filling up their tanks.

The temperature of gasoline is an important consideration. A suggestion from the insider is to only fill up in the morning, before the day’s heat has a chance to expand the gasoline.

Gasoline, stored in underground tanks, stays relatively cool, but its temperature climbs throughout day. Since gasoline is denser when cold, filling up in the morning ensures getting a full gallon for the price paid. Even one degree of temperature elevation can add up, and gas pumps do not have temperature gauges to interpret the difference.

The insider also suggests that while fueling, the highest speed on the nozzle should not be used. The faster the fuel pumps into your tank, the more vapor the process generates — vapor that gets sucked back into the storage tanks via vapor return in the hose. Slower speeds produce less vapor, allowing fewer fluids other than gas to enter the tank.

Try to fill up when the tank is still half full. If the gas tank is empty, there is more air occupying the tank. The rate at which gasoline evaporates is very high, but keeping the tank at even levels will reduce the risk of having the gas evaporate as the car’s tank fills.

A common tip is to avoid filling up when the service truck is filling the station’s underground supply. The replenishment of the underground source stirs up dirt and other particles that could potentially end up in a car’s tank.

Knowing where gas stations get their gas from is also available on the Department of Energy’s Web site. States are required to know where oil being distributed was imported from.