Sulfur trioxide (alternative spelling sulphur trioxide, also known as nisso sulfan) is the chemical compound with the formula SO3. It has been described as "unquestionably the most [economically] important sulfur oxide". It is prepared on an industrial scale as a precursor to sulfuric acid.

Thomas Loerting is an Austrian chemist and associate professor at the University of Innsbruck. His research focuses on amorphous systems, the physics and chemistry of ice and chemistry at low temperatures.