The creep theory of multipulley belt drive systems is reexamined and the belt is modeled as an elastic extensible string. An exact solution of the nonlinear steady state equations of a string is obtained which includes, elastic extension, Coulomb friction, radial and tangential accelerations, and the power loss due to friction between the belt and the pulleys. Most importantly, the present solution uses the correct compatibility condition that ensures that the same belt is considered for all applied moments and speeds. An example of a two pulley system is considered which shows that existing approximations of the compatibility condition cause previous solutions for full slip to: underpredict the maximum transmitted moment; over predict the efficiency η; and underpredict both the low and high values of the tension. [S1050-0472(00)01503-8]