Quinoline insoluble content (QI) still constitutes one of the most important physico-chemical parameters for evaluating pitches. However, quinoline is highly toxic, expensive, and the ASTM D2318 procedure is very time consuming. The solvent 1-methyl-2-pyrrolidinone (NMP) is less expensive, less toxic, and has recently become preferred as a pitch solvent by many researchers. Nonetheless, its use has not yet become standard for carbon researchers or the carbon industry because it has not been correlated with conventional QI results. The present article establishes correlations between quinoline insolubles (QI) and 1-methyl-2-pyrrolidinone insolubles (NMPI) for petroleum pitches using glass microfiber filters instead of the usual porous crucible. (c) 2008 Elsevier Ltd. All rights reserved.