Gas anchor:

A tubular, perforated device attached to the bottom of sucker-rod pump that helps to prevent gas lock.

The device works on the principle that gas, being lighter than oil, rises.

As well fluids enter the anchor, the gas breaks out of the fluid and exits from the anchor through perforations near the top.

The remaining fluids enter the pump through a mosquito bill (a tube with the anchor), which has an opening near the bottom.

In this way, all or most of the gas escapes before the fluids enter the pump.