A statistical study is performed on X-ray flares stronger than C1 class that erupted during the solar maximum between 1989 and 1991. We have investigated the flaring time interval distribution (waiting-time distribution) and the spatial correlation of successive flare pairs. The observed waiting-time distribution for the whole data is found to be well represented by a nonstationary Poisson probability function with time-varying mean flaring rates. The period most suitable for a constant mean flaring rate is determined to be 2--3 days by a Kolmogorov-Smirnov test. We have also found that the waiting-time distribution for flares in individual active regions follows a stationary Poisson probability function m exp(-mt) with a corresponding mean flaring rate. Therefore the flaring probability within a given time is given by 1-exp(-mt), when the mean flaring rate m is properly estimated. It is also found that there are no systematic relationships between peak fluxes of flares and their waiting-time distributions. The above findings support the idea that the solar corona is in a self-organized critical state. A comparison of the angular distances of successively observed flare pairs with those of hypothetical flare pairs generated by random distribution shows a positive angular correlation within ~10¿ (~180 arc sec in the observing field) of angular separation, which suggests that homologous flares occurring in the same active region should outnumber sympathetic flares. ¿ 2001 American Geophysical Union