IRAS two-color diagram for our 252 observed OH/IR stars. The red line is the evolutionary sequence for AGB stars defined by van der Veen & Habing (1988). The blue dashed line indicates the two groups of post-AGB stars, LI (left of IRAS, blue group) and RI (right of IRAS, red group) (Sevenster 2002a). The red circles indicate both SiO and H2O maser detected sources, and the green triangles and the yellow squares indicate SiO-only detected sources and H2O-only detected sources, respectively. All undetected sources are marked with a gray triangle. The sources with one-way, double-peaks, and multiple-peaks of the H2O maser are identified by their identification numbers. The identification numbers are given in Table 1.