This book analyses the process of data mining and knowledge discovery in the field of natural gas exploration in a step by step manner. The author believes the applied approach is the key to a successful data mining operation as during the research, the data used were derived from the field, the domain expert was engaged, examples are based on geoscience data and steps are described not only theoretically but also practically. So, any researcher who reads and follows the steps can feel what really a data mining procedure is. In addition, an experienced reader will find completely new concepts such as "rule usefulness" which was adopted and used in many academic articles.