Background: Onions (Allium cepa) are widely used as a flavor agent ingredient in culinary preparations to bring specific cooked onion notes. In this study, three traditional types of preparations-sué, sautéed, and pan-fried onions-were used to investigate their differences in aroma profile. Results: Headspace solid phase micro-extraction (HS-SPME) and gas chromatography (GC) coupled with mass spectrometry (MS), flame ionization detection (FID), and olfactometry were used to analyze the onion preparations. The study enables to identify 66 major compounds in the preparations. Among these compounds, sulfur compounds, aldehydes, and furans were the most represented. The pan-fried onion preparation distinguishes itself by the highest number of compounds represented in a large amount. This result is consistent with this mode of cooking that combines high temperature with long cooking time and favors the formation of compounds from the Maillard reaction and lipid oxidation. In comparison, the sué and sautéed preparations contain globally fewer compounds and, for most of them, in a lower amount compared to the pan-fried preparation. An innovative olfactometric approach was performed, based on a laboratory-developed software using an aroma wheel especially designed for the study of cooked onion. It enables an intuitive, efficient, and precise characterization of odor events along elution. A statistical comparison of intensities perceived for each odor detected during olfactometric analysis was used to understand the aroma balance and nuances perceived for these three traditional onion preparations. In accordance with chromatographic results, the pan-fried onion displays the highest number of odorant zones (65) associated with higher intensity scores and notably, to an enhanced perception of some Maillard compounds. Sué and sautéed onion profiles show an analog number of odorant zones (50 and 53), but the sautéed onion displays higher intensity scores and a particular contribution from pyrazines.