Samples of HgBa,CuO,+B (Hg-1201) were annealed under various conditions. After carefully controlling annealing time, annealing temperature (T,), and O2 partial pressure (P,), we were able to find the reversible annealing conditions for Hg-1201. Under 1 atm 0, at 260 “C~~,~400 “C, the obtained T, is nearly the same (-97 K). However, it decreases quickly with T,>300 "C in high vacuum (PO-lo-* atm), and reaches zero at T,=400 “C!. On the other hand, T, decreases with the decrease of T, in high-pressure O2 (-500 atm) and reaches -20 K at about 240 “C!. In the entire annealing region, the oxygen surplus varies significantly from 0.03 to 0.4, and a wide range of T, variation (O-+97 K-+20 K) was obtained with anion doping alone.