The degree of swelling of caustobioliths in liquids depends on their character. Correspondingly, the molecular weight M (C) of hydrocarbon chain segments between the crosslink sites, which is determined based on the Flory-Rehner or Kovac equations, changes. Based on the generalization of data on the swelling of Turkish lignites from the Goynuk deposit, it was found that the determined values of M (C) depend on the physicochemical characteristics of solvents in a complicated manner. Therefore, the values of M (C) determined in unsolvating hydrocarbons should be considered the most reliable.