The volumetric swelling procedure was applied to Goynuk and Beypazan oil shales from Turkey by using 10 solvents and the cross-linking in the macromolecular network of oil shales were investigated using this technique. Results from solvent swelling measurements show that the volumetric solvent swelling of oil shales samples roughly follows the regular solution theory. The theory of solvent swelling of cross-linked polymers developed Flory-Rehner and extension of this theory by Kovac-Peppas was used to calculate number average molecular weight per cross-link of kerogen structure ((M) over bar (c)) in oil shale samples. Results indicate no remarkable difference between (M) over bar (c) values for Goynuk oil shale (Kerogen Type I) and Beypazan oil shale (Kerogen Type II). (C) 2003 Elsevier Science Ltd. All rights reserved.