Molecular weight (MW) data for shale oils, including molecular weight distributions (MWDs) as well as average MWs, is difficult to find. A thorough literature review of MW data for shale oils from different pyrolysis processes, found scattered across a wide range of topics (or papers on various topics) and analyzed here, was carried out as part of the study. However, because the data are for oils produced under different conditions, and the exact pyrolysis conditions are sometimes not fully described, then the MW values generally are not directly comparable. Therefore, in the experimental part of the current study, average MWs and MWDs were measured for shale oils from four different oil shales (Green River in the western United States, Attarat Umm Ghudran in Jordan, Kukersite in Estonia, and Dictyonema in Estonia) obtained by retorting under identical pyrolysis conditions, using a standardized Fischer assay method. The main goal of the study, to measure the MWDs of the Fischer assay oils, was accomplished using size exclusion chromatography (SEC). The MWD data obtained was also compared to that from atmospheric solids analysis probe mass spectroscopy (ASAP MS). In addition, MWDs of industrial Kukersite shale oil from Kiviter and Galoter processes were evaluated for comparison. The MWDs of Fischer assay shale oils obtained in the current study ranged from 100 g mol(-1) to 600 g mol(-1). While the oils show comparable average MW values, the parameters describing the width and, shape of MWDs were more dependent on the parent oil shale.