2-gamma decay of the 662-keV isomer in $^{137}$Ba

2-gamma decay of the 662-keV $^{137}$Ba isomer following $^{137}$Cs beta decay has been observed using two 3"x3" NaI detectors, a 20.5-$\mu$Ci source, and a Pb shielding geometry designed to minimize direct and sequential Compton scattering backgrounds. In runs totaling 144 days, a 662-keV peak has been observed in the profile across the diagonal connecting 662-keV axis points in a 2-dimensional coincidence pulse-height spectrum. A preliminary value of $2.0(6)\times 10^{-6}$ is derived for the 2-gamma/1-gamma intensity ratio. The distribution of 662-keV events along the 2D diagonal is a continuum centered at 331-331 keV with a shape favoring a double quadrupole E2-M2 or M2-E2 decay sequence. Our result compares with upper limits of $< 10^{-5}$, our assessment of the Beusch experiment [1], and $< 2.2\times 10^{-6}$ by Basenko et al. [2]. It will be compared with theoretical estimates. \\[4pt] [1] W. Beusch, Helv Phys. Acta 33, 363 (1960)\\[0pt] [2] V.K. Basenko, A.N. Berlizov, and G.A. Prokopets, Bull. Russ. Acad. Sci. 56, 94 (1992)