<p>The production of olefins by steam cracking reactors faces significant challenges due to coke formation, which has a detrimental effect on their performance and productivity. To tackle this issue, it is crucial to enhance our understanding of fouling phenomena and their relationship with feedstock composition and process conditions. While it is widely believed that aromatics contribute to increased coke formation, our research challenges this assumption by conducting steam cracking reactions using a naphtha feedstock spiked with various aromatic compounds. It is found that the addition of benzene and toluene of up to 6 wt% in the feed results in a reduction in the total coke formation rate in the steam cracker tubes and the transfer line heat exchanger (TLE). Conversely, a 2 wt% spiking with naphthalene exhibits a minor increase in coking rate. In turn, adding a 1.2 wt% acenaphthylene shows a notable increase in the coke formation rate. However, temperature plays a pivotal role in coke formation as well, as higher temperatures are found to promote feedstock conversion and secondary reactions which contribute to coke deposition. The deposition of coke significantly increases by more than 70% in the transfer line heat exchanger for two types of feedstocks—one spiked with 3 wt% benzene and toluene and the other with acenaphthylene—due to a 20&#xa0;°C rise in temperature. In our study, we utilize the “Fouling Assessment Setup (FAST)”, an experimental unit that makes it possible to assess fouling in the cracker tubes and the TLE in a single experimental run. By employing a refinery gas analyzer (RGA) and a comprehensive gas chromatograph coupled with a flame ionization detector (GC×GC-FID), we also gather real-time information on the composition of the reactor effluent. In summary, our study underscores the significance of the full comprehension of the underlying mechanisms of coke formation in steam cracking reactors.</p>