Phosphate esters are most often used as scale control agents and metallic oxide sequestrants. As scale inhibitors, it is theorized that phosphate esters, like phosphonates, work via the crystal distortion mechanism. As the figure below depicts, these compounds are characterized by carbon to oxygen to phosphorous bonding (COP). Even though these compounds are fairly effective scale inhibitors, the major drawback associated with them is that they can rapidly revert to orthophosphate, thereby creating the potential for phosphate fouling.

The following is a diagram of a phosphate ester: