The determination of the relative concentrations of tricalcium silicate (C3S) and dicalcium silicate (C2S) within a cement sample is potentially important in the prediction of the setting properties of the cement. For model systems, we have demonstrated that the presence of a paramagnetic species in intimate (physical) contact with an otherwise diamagnetic silicon-containing mineral can dramatically decrease the longitudinal relaxation time T-1 and consequently allow for the rapid data collection of the Si-29 MAS NMR spectrum. Thus, it appears that, for cements, the T-1 values of C3S and C2S will be significantly altered because of the paramagnetic Fe3+ present in the C(4)AF matrix that makes intimate contact with each of the silicate phases. The presence of the paramagnetic C(4)AF matrix thus allows for the rapid collection of spectra of cements. Experiments that might otherwise take weeks or even months now take mere hours. Three methods of NMR relaxation have been examined and compared: inversion recovery, variable-delay Bloch decay, and saturation recovery techniques. Analysis of an API class H cement demonstrated that the saturation recovery method for analysis of Si-29 NMR data offers the best combination of accuracy, speed, and ease of processing. The saturation recovery method was used to determine the C3S/C2S ratios for eight different cements: three API class G cements and five API class H samples. Determination of C3S/C2S ratios by NMR spectroscopy provides an effective method of analysis for cements, owing to NMR spectroscopy's direct measurement of the minerals in question without the assumptions of composition that are required with oxide analysis from X-ray fluorescence and application of the Taylor-modified Bogue equations. Given the importance of C3S and C2S (and hence their ratio) in defining the performance of cements, we propose that Si-29 MAS NMR spectroscopy represents a viable method for cement characterization.