The following known beta-stable (or almost beta-stable in the case Gd) nuclides with A ≤ 260 are theoretically capable of double electron capture, where red are isotopes that have a double-electron capture rate measured and black have yet to be measured experimentally: Ar, Ca, Cr, Fe, Ni, Zn, Se, Kr, Sr, Mo, Ru, Pd, Cd, Cd, Sn, Te, Xe, Xe, Ba, Ba, Ce, Ce, Sm, Gd, Gd, Gd, Dy, Dy, Dy, Er, Er, Yb, Hf, W, Os, Pt, Hg, Rn, Rn, Ra, Th, U, Pu, Cm, Fm, and No.