When coalbeds and many other rock types containing organic matter are heated during burial, methane gas is formed as a byproduct. Methane can cause explosions in underground mines that can lead to fatalities and/or injuries to mine workers. Our objective is to design an apparatus that advances the state of the art in gas content testing equipment. It is also desirable for the new design to successfully perform gas content determinations of multiple chemical species from a rock sample. The Portable Modified Direct Method Testing Apparatus was designed, built, and developed by researchers at the National Institute for Occupational Safety and Health (NIOSH)'s Pittsburgh Research Laboratory. This new design is easier to use, rugged, compact, lightweight, reliable, and relatively inexpensive, yet provides more accurate gas content data.