A novel method for chemical fingerprinting of oil and petroleum products has recently been developed. The method is based on full-scan positive electrospray mass spectrometry (ESI-MS) using a single quadrupole LC-MS instrument, however, with direct injection (no chromatographic separation) and without fragmentation of the molecules. The aim of the present study was to establish recommended or standardized conditions able to produce mass spectrometric data of high quality with respect to pattern diversity, recognition, precision, and repeatability utilizing a standard single quadrupole ESI-LC-MS instrument. Performance was evaluated by means of Principal Component Analysis (PCA) to track changes in spectra. A mobile phase consisting of acetonitrile and 50 mM ammonium acetate (90:10) was found to give the optimum result, and instrument parameters to produce unfragmented spectra were established. The method can be considered as a first attempt to establish standardized conditions and parameters applicable to modem single quadrupole LC-MS instruments for the purpose of performing chemical fingerprinting using the combination of ESI-MS and chemometrics.