Effect of Oxygen on Zero-field NMR Oxygen molecules, being paramagnetic (i.e., containing unpaired electrons), influence nuclear spin relaxation . Therefore, to avoid oxygen-induced relaxation, liquid NMR samples are often degassed. This is achieved by purging the samples with neutral gas (e.g., nitrogen) or by the freeze-pump-thaw technique and subsequent flame sealing. Despite the fact that this procedure is routinely used, its significance on ZULF NMR spectra has never been investigated. To fill this gap, we studied this effect by analyzing the amplitudes and widths of peaks observed in zero-field NMR J-spectra , which provide information about the longitudinal (T 1 ) and transverse (T 2 ) relaxation times.