A general expression is developed for the basic circuit reliability when any number of different propagation modes may be present. This is used to formulate a full method of evaluation for two propagation modes, assuming that daily values of mode basic MUF and signal/noise ratio each follow a normal distribution. Approximations to the full method lead to the generation of a new simplified method, suitable for routine prediction application, which takes account of the correlation between mode basic MUFs. Results are presented of sample comparisons between values of reliability given by the full method, the simplified method and other existing approximate methods.