Plant oils are preserved are archaeological sites in association with unglazed pottery and botanical remains. A new methodology using electrospray-mass spectrometry (ESI-MS) has demonstrated the presence of triacylglycerols (TAG) preserved in organic extracts of Roman ceramic amphoras. Glycerids, isolated by fast solid-phase extraction (SPE) were analyzed by ESI-MS, allowing a discrimination of the samples by the mass spectrum of the lithiated adducts. The molecular structure of all the triacylglycerols and their degradation markers was studied by monitoring the low-energy collisionally activated dissociation (CAD) spectrum of the lithiated adducts. Features of tandem mass spectra of such species allow to elucidated, for the first time, by a fast and direct analysis, the complete molecular structure of the biomarkers of olive oil and their degradation markers, in order to determine the biological origin of the preserved lipids in archaeological pottery. The fast preparation of the samples followed by a rapid, very selective and sensitive analysis of the lipidic extract by direct inlet into the ESI-source permits the identification of traces of olive oil in a series of archaeological potsherds issued from shipwrecks from the ancient Roman world. This new analytical strategy appears to be a valuable method for determining the various commodities transported through the Mediterranean Sea at the time of the Roman Empire.