Mutagenicity studies were conducted on 3 petroleum fractions: rubber solvent, (identified as either a single chemical or a mixture of CAS 64742-89-8 and 64741-84-0); 60 solvent,(a blend of any or all of the following: CAS 64741-46-4, 64741-66-8, 64741-99-7, 64741-84-0, 64742-88-7, 64742-95-6), and high aromatic solvent, (either a single chemical or mixture of CAS 64742-95-6, 64742-94-5, 64741-99-7, 64741-98-6). Cytogenetic assays were conducted with male Long-Evans rats (30/group) administered 1.5 ml/kg of a negative control of 1.5 ml/kg water, or 20 mg/kg of the positive control, 7,12- dimethylbenz(a)anthracene by intraperitonal injection. Increased Type I and Type II chromosomal aberrations were observed in both and within 1 day, and showed increased Type I aberrations within 7 days post-treatment. Three-tier testing of (I) and (II) showed the following: no evidence of mutagenicity in microsome plate assays with 5 tester strains of Salmonella typhimurium and Saccharomyces cerevisiae strain D4, with and without S9; no evidence of forward mutations in the L5178Y mouse lymphoma assay; no evidence of chromosomal aberrations in the cytogenetic analysis of bone marrow cells from exposed male Sprague-Dawley rats; and no evidence of compound-induced lethality in the dominant lethal assay with rats. Ten additional petroleum fractions tested for dominant lethality to mice showed no evidence of mutagenic potential.