Gel ink pens are common writing instruments in the United States. Modern black gel inks are both pigment and dye-based and their analysis on questioned documents (QD) can be problematic. It is important from a forensic standpoint to be able to identify differences between black gel inks so that a forensic examiner can pinpoint the manufacturer of a gel pen. In the current study, 29 black gel pens from 17 different manufacturers were obtained and were used to mark on Whatman filter paper. All inks were examined under magnification for morphological differences. The optical and chemical techniques used to analyze the inks included microscopy, visible and near infrared reflectance, near infrared luminescence, thin-layer chromatography (TLC), spot tests, and gas chromatography/mass spectrometry (CG/MS). The results grouped the inks into 19 groups and a flow chart was developed that is useful in distinguishing between gel or roller-ball ink. A second flow chart differentiates open market gel inks using optical and chemical techniques. Additionally, the analysis indicated that the volatile compounds found in gel inks may contain some unique ingredients not typically found in other non-ballpoint inks. Future research should focus on similar comparisons of colored inks. Table, figures, references