Gelling agents, also known as solidifiers, are chemicals that react with oil to form rubber-like solids. With small spills, these chemicals can be applied by hand and left to mix on their own. For treating larger spills, the chemicals are applied to the oil, then mixed in by the force of high-pressure water streams. The gelled oil is removed from the water using nets, suction equipment, or skimmers, and is sometimes reused after being mixed with fuel oil.

Gelling agents can be used in calm to moderately rough seas, since the mixing energy provided by waves increases the contact between the chemicals and the oil, resulting in greater solidification.

There is one drawback to the use of gelling agents. Large quantities of the material must often be applied, as much as three times the volume of the spill. For oil spills of millions of gallons it is impractical to store, move, and apply such large quantities of material.