Publisher's Note: This book delves into the fundamentals of fuel quality assessment, outlining the principles of quality control for various types of petroleum fuels. It succinctly presents methods for evaluating physicochemical properties and their connection to the operational characteristics of fuels. The significance of categorization and the state quality mark in enhancing fuel efficiency is highlighted. The text describes comprehensive methods for the qualification assessment of fuels and their role in testing and implementing new fuel types. Targeted at engineering and technical professionals involved in evaluating the quality of petroleum fuels, this book also addresses the improvement of production technologies and the enhancement of fuel efficiency in the national economy. Related topics include: Fuels and Lubricants, A Handbook for Oil and Gas Industry Operators (available in Ukrainian), Motor Fuels from Alternative Raw Materials, and Viscosity and Plasticity of Petroleum Products.