This Letter reports simultaneous acetylene and carbon monoxide gas sensing by using a porous hollow-core waveguide. Compared to evanescent wave based gas sensors, the hollow-core waveguide can have a much better sensitivity because the majority of the light-wave energy propagating in the hollow core can interact directly with the gas molecules. The wall of the waveguide is made porous by the phase separating and leaching of the initial glass tubing. This allows the gas molecules to easily penetrate into the sensor providing the sensor with a very fast response time compared to other waveguide based gas sensors. A gas chamber system was constructed to simultaneously measure the presence of acetylene and carbon monoxide gases, and the testing results clearly indicate the high sensitivity and fast response time of this sensor.