Given the demand for clean gasoline with ultralow sulfur and olefin contents, reduced olefin content, which inevitably results in a large octane number loss, is urgently needed. The key to finding a solution for octane number loss is to identify the relationship between olefin hydrogenation and the loss of octane number of gasoline. The negative effect of certain olefins on octane number was first investigated by setting different olefins saturated in the same amount. C5-C7 olefins exhibit the most adverse effect on octane number than others. In addition, the saturation amounts of various olefins were also studied by fluid catalytic cracking (FCC) gasoline hydrogenation experiment. Given the negative effect and saturation amount, the sequence of octane number loss based on olefin hydrogenation is C5 approximate to C6 > C7 > C8 > C9 > C10, wherein C5-C7 olefins, which present high saturation amounts in the hydrogenation experiment, are the main contributing factors of octane number loss in gasoline hydrogenation. Based on the above studies, the formula of the loss of octane number was developed, which can estimate the loss of octane number of gasoline with the error range of less than 0.5 units Research Octane Number. (C) 2018 Elsevier Ltd. All rights reserved.