Rebus sic stantibus is a doctrine which, in simple terms, holds that an agreement may, when certain conditions are met, be partially or wholly abrogated. OPEC nations threaten to use this doctrine to change aggreements with oil consuming trading partners.
Scheffler, William L.
"The Politicization And Death Of Rebus Sic Stantibus,"
Syracuse Journal of International Law and Commerce: Vol. 2
, Article 5.
Available at: http://surface.syr.edu/jilc/vol2/iss1/5