The first gas pumps were built in the 1880s by the Bowser Company in Fort Wayne, Indiana, followed in 1898 by pumps that could pull fuel from an underground tank. As the automobile's popularity soared in the 1920s, service stations sprang up everywhere and the gas pump became a key promotional medium.
The early pumps were 'visible gas' pumps, with a clear glass cylinder, usually 5 or 10 gallons on top of the pump, so you could see what you were getting, or if the gas was dirty (a big problem at that time). There was a manual pump you’d pull back and forth to pump the gas out of the underground tank into the cylinder, which was 8 or 10 feet tall. From there the gas flowed by gravity down the hose into the car.
Next came the electric pump, but people still wanted to see the gas, so they had a small cylinder, called a sight glass. These pumps had a clock face that kept track of the gallons, and then the seller would have to compute the cost in their head. Finally they came out with computing gas pumps, which would tell you the cost too.
Some of the most collectible pumps are the early ones with the cylinder on top and the old clock face that keeps track of just gallons. Also in demand are the computing pumps from the 1930’s into the 1950’s, but in the 1960’s they modernized them, making them more boxy and plain. Pumps from the 1930s in particular have a lot of great art deco styling (and are very tall).