Based on both available reports and the results of experimental studies, the pores in coal chars have been divided into three groups. The first group comprises of pores with radii <7.5 nm, the second one consists of the pores with radii in the range 7.5 &LE; r &LE; 2500 nm and the third group consists of the pores with r > 2500 nm, Based on the results of the experimental study conducted for ten Polish bituminous coals, the set of equations describing volume changes of the pores with r less than or equal to 2500 is derived and discussed for slow carbonization of selected coals up to 1000degreesC. The equations describe both the transformation processes of the primary pores and the formation and development of new pores depending on the final temperature of carbonization and properties of the parent coal. These properties include the Gieseler temperatures of softening and resolidification as well as the characteristics of the chemical structure of coal organic matter. The impact of the coal's organic matter contraction and the coal's total mass loss on the pore volume (cm(3)/g) are also taken into account. (C) 2002 Elsevier Science Ltd All rights reserved.