Thermal analyses involving simultaneous thermal gravimetric analysis (TGA) and differential thermal analysis (DTA) were used to study the air oxidation of petroleum (fluid and needle cokes) and coal-tar pitch cokes. The intent of this study is to understand the relationship between the structure of carbonaceous materials and their thermal oxidation behavior in air (Part 1). A correlation between the thermal oxidative properties of cokes and their electrochemical Li-intercalation performance is discussed in the following paper (Part 2). The carbon samples were heat-treated at temperatures up to 2800°C, and three thermal parameters were determined — ignition temperature (T i), temperature maximum (T m) in the DTA curves, and the temperature at which 15% carbon weight loss was attained (T 15). The measurements showed trends that are consistent with prior reports that the active sites on the surface and not the total surface area (TSA) are responsible for the thermal behavior of the carbons. Because of the difference in the graphitizability of petroleum and pitch cokes that was obtained by heat treatment, variations in the thermal parameters were observed. Needle cokes are the most easily graphitized and this is reflected in the higher values of the thermal parameters compared to the fluid and pitch cokes.