Hydraulic fracturing, a process used to extract oil and natural gas, involves injecting a complex mixture of fluids into underground formations. These fluids contain a vast array of chemicals, raising important questions about their potential impacts on human health and the environment. Understanding this complex chemical landscape is crucial for transparency and informed decision-making. FracFocus, the national hydraulic fracturing chemical registry, provides a valuable dataset, but with over 1,400 distinct chemicals reported between 2014 and 2024, navigating this information can be challenging.
To make sense of this chemical diversity, we offer several complementary perspectives. To understand the roles these chemicals play in the fracturing process, see our page on Functional Use. While functional use provides one lens, another is to consider potential hazard classifications (in the works). Further, we classify the chemicals by basic substance classes defined by CAS scientists. However, the primary focus of this series of pages is on classifying these chemicals by their dominant chemical structure.
We adopt a classification scheme based on the work of Elsner and Hoelzer (2016)1, which organizes chemicals primarily by their core molecular structure and key functional groups, organizing by large classes such as Alcohols and Inorganic Chemicals. Within most of these broad classes, chemicals are further grouped into subgroups sharing more specific structural similarities. This structural classification is powerful because it provides a foundation for understanding not only the intended function of a chemical in hydraulic fracturing, but also its potential properties, reactivity, environmental fate, and potential risks.
The table below lists the major chemical classes reported to FracFocus. Explore each class for detailed descriptions, subgroup breakdowns, and usage statistics.
| Classification | Percent of FracFocus records2 | Present in what percentage of disclosures3 | Number of discrete CASRN4 | Reported mass (in pounds) 5 |
|---|---|---|---|---|
| Inorganic Chemicals | 25.9 % | 99.8 % | 221 | 13.7 trillion pounds6 |
| “Trade secrets” and conflicting identities | 17.3 % | 86.1 % | — | 15.5 billion pounds |
| Alcohols | 11.5 % | 92.5 % | 84 | 1.79 billion pounds |
| Insoluble inorganic materials | 7.64 % | 95.9 % | 60 | 1.72 trillion pounds7 |
| Alkoxylated Alcohols | 7.31 % | 78.5 % | 87 | 803 million pounds |
| Non-functionalized Hydrocarbons | 6.19 % | 87.0 % | 130 | 4.78 billion pounds |
| Organic Acids | 5.35 % | 64.1 % | 136 | 509 million pounds |
| Electrophilic Compounds | 3.69 % | 68.1 % | 119 | 508 million pounds |
| Cationic Surfactants | 3.65 % | 67.1 % | 74 | 650 million pounds |
| Synthetic Polymers | 3.26 % | 51.6 % | 127 | 2.13 billion pounds |
| Carboxylic Acid Esters | 1.96 % | 29.7 % | 73 | 217 million pounds |
| Biopolymers | 1.55 % | 39.3 % | 24 | 2.85 billion pounds |
| Amides | 1.54 % | 36.1 % | 36 | 99.7 million pounds |
| Amines | 1.36 % | 30.7 % | 95 | 280 million pounds |
| Organo-sulfonates and -sulfates | 0.557 % | 13.5 % | 85 | 37.1 million pounds |
| Organo-phosphorous Compounds | 0.546 % | 14.7 % | 55 | 55.4 million pounds |
| Enzymes | 0.185 % | 5.26 % | 7 | 2.56 million pounds |
| Organic – oxidizing | 0.132 % | 3.87 % | 3 | 13.1 million pounds |
| Dyes | 0.124 % | 2.75 % | 17 | 98.3 thousand pounds |
| Carbohydrates | 0.103 % | 3.06 % | 13 | 27.6 million pounds |
| Gases | 0.0726 % | 2.11 % | 2 | 1.69 billion pounds |
| Unclassified | 0.00452 % | 0.136 % | 12 | 436 thousand pounds |
Footnotes
- Elsner and Hoelzer, 2016. Quantitative Survey and Structural Classification of Hydraulic Fracturing Chemicals Reported in Unconventional Gas Production. Environmental Science and Technology. 3290-3314. DOI: 10.1021/acs.est.5b02818. ↩︎
- Based on a Jan. 2025 download from FracFocus. All disclosures without chemical records (roughly 2011-mid 2013) are excluded. Duplicate disclosures and records are excluded. Records that do not report chemicals (such as “systems approach” product records) are excluded. Sorted by overall frequency. ↩︎
- Percent of the total FracFocus disclosures of fracking jobs between Jan 1, 2014 and Dec 31, 2024 that report at least one member from the indicated group. ↩︎
- CASRN are the authoritative Chemical Abstract Service Registration Numbers. Distinct numbers refer to materials that have distinct chemicals definitions in the CAS system. Note that not all materials with a CASRN are well defined. Twenty percent of FracFocus-reported materials cannot be given a “substance class” by CAS scientists because of their ambiguous or variable nature. ↩︎
- Mass summaries include only those records with valid and complete information – roughly about 80% of the records in FracFocus. See documentation for details. ↩︎
- Includes 7732-18-5 (water), the primary carrier. ↩︎
- Includes 14808-62-7 (sand), the primary proppant. ↩︎