Next we compare the spectra detected while continually bubbling parahydrogen gas during signal acquisition to the ones in which gas flow was stopped before signal acquisition was started. This comparison clearly shows that in high-field NMR (Fig. ) the sample heterogeneity induced by bubbling gas through the sample reduces the spectral resolution dramatically compared to homogeneous samples. We repeated these experiments at zero-field, with the heterogeneous-sample experiment performed in the titanium tube using 10 bar of parahydrogen gas. The results shown in Fig. clearly demonstrate that in ZULF NMR the spectral resolution is largely immune to heterogeneities produced by gas bubbling during signal acquisition.