Petroleum pollution is a major environmental problem that threatens aquatic and terrestrial ecosystems. Chemical fingerprinting is an effective analytical approach for identifying potential sources of petroleum contamination by examining the chemical composition of pollutants. This article reviews the role of petroleum hydrocarbons, polycyclic aromatic hydrocarbons (PAHs), and biomarkers in source identification, with particular emphasis on gas chromatography–mass spectrometry (GC–MS). Environmental weathering, including evaporation and biodegradation, can alter petroleum composition and complicate source identification. Integrating chemical analysis with appropriate sampling and quality-control procedures can improve the reliability of environmental investigations and support pollution management. Introduction Petroleum activities, including extraction, transportation, refining, and storage, can release hydrocarbons into soil and water. These pollutants may persist in the environment and adversely affect ecosystems. Identifying the source of contamination is essential for effective monitoring, remediation, and environmental protection. Chemical Fingerprinting and Source Identification Chemical fingerprinting identifies petroleum sources by comparing the chemical profiles of contaminated samples with those of suspected sources. Important indicators include saturated hydrocarbons, polycyclic aromatic hydrocarbons (PAHs), and petroleum biomarkers such as hopanes and steranes. Gas chromatography–mass spectrometry (GC–MS) is widely used to separate and identify these compounds. Comparing their distribution and relative abundance can reveal similarities and differences between samples and help determine potential pollution sources. Environmental Factors and Analytical Challenges Environmental processes such as evaporation, dissolution, biodegradation, and photo-oxidation can change petroleum composition. These changes may reduce the reliability of some chemical indicators. Therefore, accurate source identification requires suitable sampling, sample preservation, validated analytical methods, and quality-control procedures. Environmental Significance Chemical fingerprinting supports oil-spill investigations, pollution monitoring, contaminated-site assessment, and environmental forensic studies. It can provide scientific evidence to support environmental management and remediation decisions. However, chemical similarity alone does not conclusively establish a source; findings should be evaluated alongside other chemical evidence and investigation results.