Triethyloxonium tetrafluoroborate is the organic oxonium compound with the formula [(CH₃CH₂)₃O]BF₄. It is often called Meerwein's Reagent after its discoverer Hans Meerwein. Also well known and commercially available is the related trimethyloxonium tetrafluoroborate. The compounds are white solids that dissolve in polar organic solvents. They are strong alkylating agents. Aside from the BF₄^- salt, many related derivatives are available.