Sulfation (sometimes spelled sulphation in British English) is the chemical reaction that entails the addition of SO₃ group. In principle, many sulfations would involve reactions of sulfur trioxide (SO₃). In practice, most sulfations are effected less directly. Regardless of the mechanism, the installation of a sulfate-like group on a substrate leads to substantial changes.

Sulfation is a process used to remove "sulfur" from the combustion of fossil fuels. The goal is to minimize the pollution by the combusted gases. Combustion of sulfur-containing fuels releases sulfur dioxide, which, in the atmosphere, oxidizes to the equivalent of sulfuric acid, which is corrosive. To minimize the problem, the combustion is often conducted in the presence of calcium oxide or calcium carbonate, which, directly or indirectly, bind sulfur dioxide and some oxygen to give calcium sulfite. The net reaction is:

or the net reaction is sulfation, the addition of SO₃:

In the idealized scenario, the calcium sulfate (gypsum) is used as a construction material or, less desirably, deposited in a landfill.

Sulfation is widely used in the production of consumer products such as detergents, shampoos, and cosmetics. Since the sulfate group is highly polar, its conjugation to a lipophilic "tail" gives surfacant-like properties. Well known sulfates are sodium lauryl sulfate and sodium laureth sulfate.

Alkylsulfate are produced from alcohols by reaction with chlorosulfuric acid:

Alternatively, alcohols can be sulfated to the half sulfate esters using sulfur trioxide. The reaction proceeds by initial formation of the pyrosulfate:

Several million tons of fatty acid sulfates are produced in this way annually. The most common example is sodium dodecylsulfate (SDS) derived from lauryl alcohol.