^Rapier, Robert. Power Plays: Energy Options in the Age of Peak Oil. Apress. March 30, 2012 (March 27, 2012). ISBN 978-1430240860.请检查|publication-date=中的日期值 (帮助)
^Heshelow, Kathy. Investing in Oil and Gas: The ABC's of DPPs (Direct Participation Program). Iuniverse Inc. 2008: 52September 2, 2008. ISBN 978-0595531929.