Petroleum and biogas microbiology is the branch of microbiology that studies microorganisms capable of metabolizing or transforming crude or refined petroleum products. The microbiologist has joined many other technologists serving the oil industry. Hydrocarbons and their derivatives (especially oxygenated and chlorinated), both natural and xenobiotic, are a very large class of compounds whose conversions and degradation by microorganisms cover a very rich field, the basic concepts of which are covered in detail in this course. The impressive evolution of these concepts over the past twenty years has revealed the scale of environmental processes and expanded their industrial applications. By the end of the course, students will have acquired knowledge and skills to advance their interest in hydrocarbon conversion by microbial activity, microbial metabolism of hydrocarbon-utilizing bacteria, and microbial ecology.