Petrographic and geochemical results of a study carried out on a suite of samples from the Silurian Qusaiba Member of the Qalibah Formation in Saudi Arabia were evaluated in order to determine how the vitrinite-like reflectance of graptolites and chitinozoans (zooclasts) relates to other organic geochemical data. The sample set includes a range of maturities from immature (less than or equal to 0.5% VRe) to post-oil-expulsion mature (0.9-1.0% VRe) as determined from pyrolytic data (T-max from Rock-Eval pyrolysis), thermal alteration index (TAI), and liptinite fluorescence. Data compiled in this study indicate that the reflectance values measured on graptolite and chitinozoan fragments were higher than equivalent vitrinite reflectance based on other geochemical maturity indicators. For example, pyrolysis T-max and biomarker maturity indicators that indicated immaturity for the Silurian source rock had a graptolite and chitinozoan reflectance of more than 0.6%. A well that had a maturity equivalent of about 0.9% vitrinite reflectance at the source rock horizon had a graptolite and chitinozoan reflectance of 1.2%. Because of this discrepancy between the reflectance of graptolites and chitinozoans and other maturity indicators, an attempt was made to determine what factors may control the reflectance of graptolites. If it is assumed that the graptolites and chitinozoans act like vitrinite during maturation, then one reason for the discrepancy between the measured graptolite and chitinozoan reflectance and the vitrinite reflectance equivalents from conventional maturity indicators may be due to the environmental conditions during deposition or preservation of the organic matter. At the immature to early mature sites, the source rocks that were deposited under dysoxic conditions had higher random reflectance values than the site deposited under anoxic conditions.