X-ray emission is modeled and x-ray intensities are predicted for Venus and Mars. Two emission mechanisms are studied: (1) elastic scattering of solar x-rays by atmospheric neutrals, (2) absorption of solar x-rays in either the carbon or oxygen K-shells followed by fluorescent emission of x-rays. The carbon and oxygen atoms reside in the carbon dioxide molecules. We predict total soft x-ray intensities of approximately 0.67 R for Venus and 0.15 R for Mars, corresponding to total soft x-ray luminosities of about 35 MW and 2.5 MW, respectively. These luminosities exceed the x-ray luminosities expected from the solar wind charge exchange mechanism. ¿ 2001 American Geophysical Union