When lava flows and pyroclastic deposits exhibit sufficient porosity and permeability, extrusive igneous rocks have the potential to host large hydrocarbon accumulations. The porosity in these deposits can come from either vesicular porosity, or from secondary porosity that resulted from later fracturing and hydrothermal alteration. Recent studies (Feng, 2008) show that significant hydrocarbon reserves are contained in volcanic rocks in China which are primarily found in the Songliao, Bohai Bay, and Erlian basins. These hydrocarbon-rich reservoirs range from upper Jurassic to Tertiary in age.