A time projection chamber with 8.3 grams of enriched (100MoO3)-Mo-100 as the central electrode has been operating approximately five months in an underground laboratory. A preliminary analysis of the two-electron sum energy spectrum, the spectrum of those same electrons taken singly, and the opening angle distribution yields a half life of 1.16(-0.08)+0.34 x 10(19) y at the 68% confidence level for two-neutrino double beta decay of Mo-100.