Automatic chainsaw oilers utilize a pump and plunger assembly to push the oil into the groove around the bar. As the chain moves around the bar, it forces the oil around the rest of it.
How the oil is dispersed varies depending on the chainsaw model; some have a separate pump to move the oil, while others utilize the crankshaft assembly. The oil is stored in a reservoir, and as the chainsaw operates, the plunger assembly pushes the oil up into the bar of the chain. As the chain moves around the bar, the oil lubricates both the chain and the bar.