Recycled oil has emerged as a big food safety issue and poses a major threat towards the public health. To date, very limited studies have been conducted to detect the adulteration of used and recycled palm olein in refined, bleached, and deodorized palm olein (RBDPO). In this study, oil samples that underwent controlled heating and deep-frying studies were refined using the common oil refining procedure to simulate the production of recycled oil. Polymerized triacylglycerol (PTG), oxidized monomeric triacylglycerols (oxTAGs), such as epoxy, keto, and hydroxy acids, and caprylic acid have been proposed as potential indicators to track the adulteration of recycled oil.For PTG, triacylglycerol oligomers and dimers showed a significant increase (p < 0.05) after the refining process. Although there was a significant reduction (p < 0.05) in the total oxTAGs concentration after refining, they were still present in the recycled palm olein, even though the used palm olein had undergone a complete oil refining process. Caprylic acid's concentration increased significantly (p < 0.05) in palm olein after undergoing various heat and deep-frying treatments and even showed a significant (p < 0.05) increase in recycled oil.The results justified the suitability of the proposed quality parameters to be used as quality indices to control the adulteration of used and recycled palm olein in RBDPO for the protection of the health and safety of consumers. This article is protected by copyright. All rights reserved.