The production of C+ in a microwave ion source injected with a gaseous CO2 sample has been investigated as an alternative to sample graphitization. A continuous flow of argon gas maintained the discharge, and 20 μL of CO2 gas at approximately 1 atm was pulsed into the source through a sample valve closely coupled to the plasma chamber. The C+ component of the beam fell to 1% of its original intensity less than 10 s after the valve was operated. In a separate experiment, the microwave ion source was operated with pure CO2 feed gas and the extracted beam was magnetically analyzed. Efficient breakup of the molecules was observed. These results are considered promising for such applications as accelerator mass spectrometry of C isotopes in gaseous samples.