This series consists of files representing research on individual works listed in the Catalogue Raisonée. The folders are ordered sequentially by catalogue entry number, beginning with Volume 1 and continuing through Volume 4. Note that not every work shown in the catalogue is represented here, and that often files yield very little information beyond what is already available in the published catalogue. Many of the files include prints, slides, and other types of transparencies of varying degrees of quality. Some of these images served as the source for the images published in the catalogue. DVDs holding digital images of the works are found in the Digital media series. Other materials found here may include correspondence with museums, galleries, archives, and individuals about a work's physical features and provenance; original catalogue entry worksheets completed in the early years of the project; authenticity reports commissioned by owners, auction houses, galleries, and museums; and photocopies of archival and other materials that refer to physical aspects of the work, provide biographical information about its subject, or furnish information about Chase during the period when he created the work. A list of works not represented in this series may be obtained from the Kellen Design Archives.

The numbering system for objects continued after publication of the first three volumes of the catalogue raisonee, first for additions that were added as an addendum in Vol. 4 (Medium, A – for addendum, then number, e.g., OPA.602. Works added after the final volume was published have a second A (for archives) added to the system – e.g. OPAA.613.