Triosmium dodecacarbonyl catalyzes a very efficient oxidation of alkanes by H2O2 in MeCN to afford alkyl hydroperoxides (primary products) as well as alcohols and ketones (aldehydes) at 60 degrees C if pyridine is added in a low concentration. Turnover numbers attain 60 000, and turnover frequencies are up to 24 000 h(-1).