The absorption spectrum of ethane was measured by frequency-stabilized cavity ring-down spectroscopy over the wave number range 5950–5967cm−1. Spectra are reported for both pure ethane acquired at pressures near 3Pa and mixtures of ethane in air at pressures ranging from 666Pa to 101.3kPa. Absorption cross sections are reported with a spectrum sampling period of 109MHz and frequency resolution of 200kHz. Atmospheric pressure cross sections agree fairly well with existing cross sections determined by FTS in nitrogen, but there are significant variations in cross sections at lower pressures. Source identification of fugitive methane emissions using spectroscopic measurements of the atmospheric ethane-to-methane ratio is also discussed.