A hyphenated method for Os isotope ratio measurements by double focusing, sector field ICP-MS (ICP-SFMS) was developed. The method is based on several optimised, concurrent processes: Os extraction from samples in hot concentrated nitric acid; separation of Os from the digest solution by formation of volatile osmium tetroxide accelerated by continuous hydrogen peroxide addition; transport of analyte vapour by an oxygen flow into the ICP; and isotopic analysis by ICP-SFMS. Due to the very efficient analyte utilisation (in excess of 0.5‰), isotope ratio measurement can be performed at low pg Os levels. Combined with the ability to process sample sizes up to 2 g (up to 50 g if the organic matrix of biological or botanical samples is eliminated by ashing), materials with Os concentrations in the low, or even sub-pg g-1 range can be analysed by the method. This ability was used to measure Os concentrations and isotope ratios in variety of environmental and geological materials. Based on the data, it was possible to trace both long-range and local Os emission sources.