<p>This work assesses the possible uses of a byproduct derived from oil sludge and palm kernel shell waste co-gasification. The thermochemical conversion process was performed in a reverse downdraft gasifier, varying the airflow from 30 to 60 L/min to produce four char samples (F30, F40, F50, and F60). The char chemical composition was determined by proximate and ultimate analyses, higher heating value, and x-ray fluorescence (XRF). Scanning electron microscopy (SEM) and Brunauer, Emmett, and Taller (BET) surface area techniques were utilized to evaluate the char’s physical structure. The results indicated that the char samples had a high carbon (40.37 to 53.33%) attributed to the participation of fossil waste in the gasification process. Furthermore, the XRF analysis indicated the presence of silicon, potassium, and calcium, which are essential soil micronutrients if the char is used as a soil conditioner. The SEM analysis showed that F50 had a less fibrous cell wall and a carbonaceous surface that was more defined due to the oxidation reaction at higher gasification temperatures, while F30 and F40 had fibrous and porous structures, respectively. The SEM analysis agreed with the BET surface area since F50 presented a higher value (269.8 m²/g) due to the formation and widening of micropores and mesopores. Therefore, the physicochemical characterization and surface structure assessment are essential to explore the possible uses of char (such as soil amendment, carbon sequestration, activated carbon, and fuel) as a value-added co-product, seeking to contribute to the sustainability and circular economy of the petroleum and palm oil industries.</p>