Chemical sensors are attracting tremendous interest because of their extensive applications for environmental analysis, especially with the increasing concern of the global warming. Problems encounter with commonly used gas sensing materials are lack of flexibility, poor response times and operated at elevated temperature. Carbon nanotubes (CNTs) have aroused worldwide excitement since their discovery because of their remarkable mechanical, electrochemical, physical and chemical properties. These important properties of CNTs provide a potential for developing sensors with high sensitivity, shorter response time and low operating voltage. This book, therefore, provides a chemical method to produce CNTs on quartz substrate using different hydrocarbon sources. The synthesized CNTs will be used to fabricate thin film chemical sensors. In addition, the effect of gas adsorption towards electrical resistance of CNTs will be investigated. The findings should be especially useful to professionals in Nanotehnology field, or industries which may be considering utilizing CNTs for gas detection.