This data set contains ethane, propane, and n-butane measurements in firn air from the South Pole and the West Antarctic Ice Sheet (WAIS) Divide in Antarctica, and from Summit, Greenland. The WAIS Divide and South Pole samples were collected in December to January of of 2005/06 and 2008/09, respectively. The Summit firn was sampled in the summer of 2006. Analyses were conducted on a gas chromatography - mass spectrometry (GC-MS) system at the University of California, Irvine. Measurements and the associated uncertainties are reported as dry air molar mixing ratios in part per trillion (ppt). The reported measurements for each sampling depth represent a mean of multiple measurements on more than one flask in most cases. Data are available via FTP in Microsoft Excel (.xls) format.