A History of the Railway Mail Service, Columbian Correspondence Course, Washington, D.C., 1903 (reprint), Mobile Post Office Society, Omaha, Nebraska, 1977

Bergman, Edwin B., 29 Years to Oblivion, Mobile Post Office Society, Omaha, Nebraska, 1980

German, William (editor), The William Wyer Collection of Railroad and Inland Waterways Covers, Classic Arts Press, 1978

Handy Railroad Atlas of the United States (reprint) Model Craftsman Publishing Corp., Fredon, New Jersey); Rand, McNally & Co., Chicago, New York & San Francisco, 1973

Kay, John L., Directory of Railway Post Offices, Mobile Post Office Society, Lexington, Georgia., revised 1997

Long, Bryant Alden & Dennis, William Jefferson, Mail by Rail, Simmons-Boardman, New York, 1951

MacDonald, Fred, United States Transit Markings Catalog (Vol. IV – Rail Agents & Transfer Clerks c.1845-c.1971) - including work originally done by Charles L. Towle - Mobile Post Ofice Society, 1996 edition

MacDonald, Fred & Towle, Charles L., United States Railway Post Office Postmark Catalog, Mobile Post Office Society, Constook, New Hampshire, published serially: Vol. I, 1990; Vol. II, 1991; Vol. 3, 1992

MacDonald, Fred & Towle, Charles L., United States Railway Post Office Postmark Catalog 1864 to 1977, Vol. I (revised 2001 serially), Mobile Post Office Society, Holmdel, New Jersey

Mehrer, Jim, Cross-reference Guide to United States Railway Post Office Postmarks (revision 2), published by the author (photcopy), Rock Island, Illinois, 1994

Modelski, Andrew M. (compiler), Railroad Maps of the United States, Library of Congress, Washington, D.C., Washington, D.C.

Morgan, Dale L., Pioneer Atlas of the American West, Rand, McNally & Co., Chicago, New York & San Francisco, 1956

Official Guide of the Railways, various monthly issues through 1971

Remele, C. W., United States Railway Postmarks 1837 to 1861, American Philatelic Society, State College, Pennsylvania, 1958

Rohrer, D. J., There Were Stars in Those Cars (illustrations by Nancy B. Clark), Mobile Post Offiice Society, Lexington, Georgia, 1992

Towle, Charles L. & Meyer, Henry A., Railway Postmarks of the United States 1861 to 1886, U. S. Philatelic Classics Society Inc., Federalsburg, Maryland, 1968

Towle, Charles L., U.S. Route and Station Agent Postmarks (with subsequent addenda), Mobile Post Office Society, Tucson, Arizona, 1986

Towle, Charles L., United States Transit Markings Catalog 1837 to 1974 – (Vol. I, 1837-1886), Mobile Post Ofice Society, Omaha, Nebraska, 1975

Towle, Charles L., United States Transit Markings Catalog 1837 to 1974 – (Vol.II, 1887-1974, A to L), Mobile Post Ofice Society, Omaha, Nebraska, 1977

Towle, Charles L., United States Transit Markings Catalog 1837 to 1974 – (Vol.III, 1887-1974, M to Z), Mobile Post Ofice Society, Omaha, Nebraska, 1979-1981

Towle, Charles L., United States Transit Markings Catalog (Vol. IV – Rail Agents & Transfer Clerks c.1845-c.1971), Mobile Post Ofice Society, Holmdel, New Jersey, 1982

White, James E., A Life Span and Reminissences of Railway Mail Service, Black Letter Press, Grand Rapids, Michigan, 1973

Wright, Norman E., Selected Rochester (N.Y.) Rail Mail (a philatelic gold medal exhibit by the author), Rochester, New York, 1995

…and a personal collection of RPO covers and other philatelic literature and ephemera related to the above.