The following known beta-stable (or almost beta-stable in the cases Ca, Zr, and Rn) nuclides with A ≤ 260 are theoretically capable of double beta decay, where red are isotopes that have a double-beta rate measured experimentally and black have yet to be measured experimentally: Ca, Ca, Zn, Ge, Se, Se, Kr, Zr, Zr, Mo, Mo, Ru, Pd, Cd, Cd, Sn, Sn, Te, Te, Xe, Xe, Ce, Nd, Nd, Nd, Sm, Gd, Er, Yb, W, Os, Pt, Hg, Po, Rn, Rn, Ra, Th, U, Pu, Cm, Cf, Cf, and Fm.