API Spec 13A sets requirements and test procedures for 13 commodity drilling fluid materials, and its current edition is the 19th edition (2019) with Addendum 1 (2020), Addendum 2 (2022) and Errata 1 (2024) (API Standards Plan, checked 2026-10-27). The American Petroleum Institute (API) names the grades that the weighting minerals, clays and polymers of a drilling fluid are sold to, from barite and bentonite to polyanionic cellulose and drilling-grade xanthan gum.
ISO 13500:2008, with Cor 1:2009 and Amd 1:2010, is the ISO counterpart of the API text, and a 20th edition of API Spec 13A is in development. The two documents carry different dates and are cited separately.
The specification groups its 13 materials into two weighting agents, six viscosifiers and five fluid-loss materials, and it adds general clauses on records, calibration, packaging and marking, ten precision tables and three reference materials. API sells the full text; the three amendments are free of charge from API.
Standards and regulations are checked against their issuing bodies, product values against the named data sheet and figures against the dated source named in the sentence; see our methodology and fact-checking.
The key facts of API Spec 13A are summarized in the table below.
| Fact | API Spec 13A |
|---|---|
| Instrument type | API Specification ("shall" requirements), not a Recommended Practice |
| Title | Drilling Fluid Materials |
| Publisher | American Petroleum Institute, listed by the API Committee on Standardization of Oilfield Equipment and Materials |
| Base text | 19th edition, published 2019-10-10 |
| Amendments | Addendum 1 (2020-04-14), Addendum 2 (2022-06-23), Errata 1 (February 2024) |
| Next edition | 20th edition in development, no date |
| Materials covered | 13 (barite counted once, in two density grades) |
| ISO counterpart | ISO 13500:2008 with Cor 1:2009 and Amd 1:2010 (ISO/TC 67/SC 3) |
| Review cycle | At least every 5 years, with one extension of up to 2 years |
What Is API Spec 13A?#
API Spec 13A is a Specification, so its clauses are "shall" requirements for manufacturers of named commodity products, unlike API RP 13B-1, 13B-2, 13D and 13I, which are Recommended Practices. Its title is "Drilling Fluid Materials" (API Standards Plan), and the API Committee on Standardization of Oilfield Equipment and Materials lists it with the rest of the 13 series. The difference matters in a contract: a Specification states pass or fail limits for a product, while a Recommended Practice describes how to test or run a fluid.
The specification covers commodity materials only and excludes single-source, limited-source and speciality products (18th edition (2010) text). Commodity status explains the short material list: a proprietary polymer blend or a branded lost circulation pill has no API grade and is bought on its own data sheet. API reviews each of its standards at least every five years and then revises, reaffirms or withdraws it, with a one-time extension of up to two years.
Who uses API Spec 13A?#
Manufacturers test each lot of barite, clay or cellulose polymer against the material clause, and buyers name the grade in a quote and check the certificate of analysis per lot. The text states that it is intended for the use of manufacturers of named products (18th edition (2010) text).
Buyers write the edition, the material clause and the grade into an order, which is what an API 13A grade in a quote means in practice. Manufacturers who want the API Monogram on their sacks take a separate, voluntary step: the API Monogram is a licensing program, a licensee runs an API Spec Q1 quality system, and the mark goes only on new product that conforms and comes from a licensed facility. Licensees are searchable by specification and product in the API Composite List.
Which Edition of API Spec 13A Is Current?#
API Spec 13A, 19th edition (2019) with Addendum 1 (2020), Addendum 2 (2022) and Errata 1 (2024), is the current edition (API Standards Plan, checked 2026-10-27); a 20th edition is in development. The 19th edition base text was published on 2019-10-10, and three amendments have followed it, each issued as a separate document that a reader applies to the base text. The API Standards Plan gives no date for the 20th edition.
The edition chain of API Spec 13A, from the OCMA specifications to the pending 20th edition, is listed in the table below.
| Date | Document | What changed |
|---|---|---|
| 1983 | OCMA specifications | Submitted to API; origin of OCMA-grade bentonite and the API standard evaluation base clay |
| 2004-02-01 | 16th edition | Basis of ISO 13500 |
| February 2010 (effective 2010-08-01) | 18th edition | Barite 4,1 added as clause 20 |
| 2019-10-10 | 19th edition | Current base text |
| 2020-04-14 (Monogram effective 2020-10-01) | Addendum 1 | OCMA-grade bentonite as clause 19 with Table 18; precision Table B.5 |
| 2022-06-23 (Monogram effective 2022-12-01) | Addendum 2 | Clause 6 packaging and marking; barite Table 2; Annex A removed; Annex B replaced; Annex D reference materials |
| February 2024 | Errata 1 | Reagent of paragraph 18.3.2.2 replaced by borax |
| Pending | 20th edition | In development, no date |
What Addendum 1, Addendum 2 and Errata 1 changed#
Addendum 1 (April 2020, API Monogram effective 2020-10-01) returned OCMA-grade bentonite to the specification as clause 19 with Table 18 and added precision Table B.5 for it. OCMA-grade bentonite had been clause 11 of the 18th edition (2010).
Addendum 2 (June 2022, API Monogram effective 2022-12-01) replaced the packaging and marking clause 6, replaced barite Table 2 with the grades Barite 4.2 g/mL and Barite 4.1 g/mL, removed Annex A (API Monogram), replaced the Annex B precision tables and added Annex D on reference materials. It also changed the introduction, the scope and subclause 5.2.11, while the hematite requirement table and clauses 14 to 18 stayed untouched.
Errata 1 (February 2024) replaced the reagent in paragraph 18.3.2.2 with sodium tetraborate decahydrate (borax), the guar-detection reagent of the drilling-grade xanthan gum clause. That correction places drilling-grade xanthan gum in clause 18 of the 19th edition.
Earlier editions and the OCMA origin#
The Oil Companies Materials Association (OCMA) and its successor committees were declared defunct, and their specifications went to API in 1983. That transfer is the origin of OCMA-grade bentonite and of the API standard evaluation base clay, formerly called OCMA base clay.
ISO 13500 is substantially based on the 16th edition of API Spec 13A, dated 2004-02-01. The 18th edition (February 2010, effective 2010-08-01) carried Barite 4,1 as clause 20 and was the API text of ISO 13500:2008 with Cor 1:2009. Neither edition is current, and their clause numbers differ in places from the 19th edition.
Which Materials Does API Spec 13A Cover?#
API Spec 13A covers 13 materials: two weighting agents (barite in two density grades and hematite), six viscosifiers (bentonite, non-treated bentonite, OCMA-grade bentonite, attapulgite, sepiolite and drilling-grade xanthan gum) and five fluid-loss materials (CMC-LVT, CMC-HVT, starch, PAC-LV and PAC-HV). Each group belongs to one additive class: weighting agents raise mud density, viscosifiers build viscosity and gel strength, and fluid-loss materials reduce the filtrate a mud loses to permeable rock. CMC is carboxymethyl cellulose and PAC is polyanionic cellulose, each in a low-viscosity and a high-viscosity grade.
The 13 materials, their grade names, their class and their clause in each edition are compared in the table below.
| Material | API grade or variant name | Additive class | 19th-edition clause | 18th edition (2010) clause |
|---|---|---|---|---|
| barite | Barite 4.2 g/mL, Barite 4.1 g/mL | Weighting agent | 7 (Table 2 as replaced by Addendum 2) | 7 and 20 (Barite 4,1) |
| hematite | Hematite | Weighting agent | 8 | 8 |
| bentonite | Bentonite | Viscosifier | Cited by 18th-edition number | 9 |
| non-treated bentonite | Non-treated bentonite | Viscosifier | Cited by 18th-edition number | 10 |
| OCMA-grade bentonite | OCMA-grade bentonite | Viscosifier | 19 (Addendum 1, Table 18) | 11 |
| attapulgite | Attapulgite | Viscosifier | Cited by 18th-edition number | 12 |
| sepiolite | Sepiolite | Viscosifier | Cited by 18th-edition number | 13 |
| CMC-LVT | Low-viscosity carboxymethyl cellulose | Fluid-loss material | Cited by 18th-edition number | 14 |
| CMC-HVT | High-viscosity carboxymethyl cellulose | Fluid-loss material | Cited by 18th-edition number | 15 |
| starch | Starch | Fluid-loss material | Cited by 18th-edition number | 16 |
| PAC-LV | Low-viscosity polyanionic cellulose | Fluid-loss material | Cited by 18th-edition number | 17 |
| PAC-HV | High-viscosity polyanionic cellulose | Fluid-loss material | Cited by 18th-edition number | 18 |
| drilling-grade xanthan gum | Drilling-grade xanthan gum | Viscosifier | 18 (Errata 1) | 19 |
Requirement values are on each material page; organophilic clay has no API Spec 13A section.
The term "API 13A grade" applies only to these 13 materials. Organophilic clay has no section in the 19th edition with Addenda 1 and 2, and none of the 13 materials is a lost circulation material or a shale inhibitor (18th edition (2010) text). Each material page carries its requirement values, labeled "18th edition (2010) text" for bentonite, attapulgite, sepiolite, CMC, starch, polyanionic cellulose and xanthan gum, and "18th edition (2010) value, unchanged by Addendum 2" for hematite.
How Is API Spec 13A Structured?#
API Spec 13A is built as general clauses (records, calibration, packaging and marking) followed by one clause per material and annexes for precision and reference materials. Its normative references are ISO 6780, ISO 10414-1, ASTM D422, ASTM E11, ASTM E77, ASTM E161 and ASTM E177 (18th edition (2010) text). Manufacturers keep records for at least five years (18th edition (2010) text, 4.3), and Annex A has been blank since Addendum 2, pointing to Annex A of API Spec Q1.
The parts of the specification and the amendment that last changed each one are listed in the table below.
| Part | Content | Changed by |
|---|---|---|
| Normative references | ISO 6780, ISO 10414-1, ASTM D422, E11, E77, E161, E177 | 18th edition (2010) text |
| 4.3 | Records kept at least 5 years | 18th edition (2010) text |
| 5.2.11 | In-house calibration against reference materials | Addendum 2 |
| 6 | Packaging and marking | Addendum 2 |
| 7 to 19 | One clause per material | Addendum 1 (clause 19), Errata 1 (18.3.2.2) |
| Annex A | Intentionally blank; see API Spec Q1 Annex A | Addendum 2 |
| Annex B | Precision tables B.1 to B.10 | Addendum 1 (B.5), Addendum 2 (replaced) |
| Annex D | Reference materials | Addendum 2 |
Precision tables in Annex B#
Annex B holds ten precision tables, B.1 to B.10, giving repeatability and reproducibility at 95 % confidence from API interlaboratory studies of 1988 to 1992 (API Reports 88-30, 89-30, 90-30 and 92-30). Repeatability is the spread within one laboratory, and reproducibility is the spread between laboratories. Each material page carries its own precision values, and an acceptance dispute between a supplier and a buyer is settled against the reproducibility limit.
The Annex B table that belongs to each material is mapped in the table below.
| Table | Material |
|---|---|
| B.1 | Barite |
| B.2 | Hematite |
| B.3 | Bentonite |
| B.4 | Non-treated bentonite |
| B.5 | OCMA-grade bentonite |
| B.6 | Attapulgite |
| B.7 | Sepiolite |
| B.8 | CMC-LVT |
| B.9 | CMC-HVT |
| B.10 | Starch |
Annex B precision at 95 % confidence, from API interlaboratory studies of 1988 to 1992.
Packaging and marking under clause 6#
Clause 6, as replaced by Addendum 2 (2022), lists four forms of supply (bulk pneumatic delivery, bulk bags, multi-wall paper sacks and cardboard boxes) and limits palletized loads to 80 in. (2.0 m) height and 4,400 lb (2,000 kg) net mass per pallet unless agreed. Overhang is at most 1.2 in. (30 mm), and pallets follow ISO 6780. Bulk deliveries are marked on the bill of lading, and barite is marked "Barite 4.x g/mL" or with a trade name, with its net mass and a lot traceable to the producing facility and country of origin.
How Do Manufacturers Show Conformity with API Spec 13A?#
A manufacturer shows conformity with API Spec 13A on a composite sample that represents no more than one day's production and is controlled by the manufacturer (Addendum 1, 2020). The composite sample must meet the material's requirement table and represent the product produced, which ties every certificate of analysis to one day of output or less.
Laboratories also prove that their own test results are sound. Under subclause 5.2.11 of Addendum 2, in-house results on the reference materials must fall within the Annex B reproducibility limit of the certificate or label value of that reference material.
Reference materials for calibrating test results#
API Spec 13A uses three reference materials, and Annex D (Addendum 2, 2022) describes them. The three reference materials and their use are listed below.
- Test calibration barite: checks barite density results; API's calibration barite, lot 005, reads 4.22 g/mL with an acceptable range of 4.19 to 4.25 g/mL.
- Reference calibration bentonite: checks bentonite test results and is run at least once per 40 tests (Addendum 1).
- API standard evaluation base clay: the clay of the polyanionic cellulose test fluid (18th edition (2010) text), a different material from OCMA-grade bentonite.
Reference calibration bentonite lot 6-2013 has a YP/PV ratio of 0.84 with an acceptable range of 0.59 to 1.09 (Addendum 2, Table B.12). A laboratory result on that lot outside the range fails the calibration check of subclause 5.2.11.
The base clay and OCMA-grade bentonite share the OCMA origin but serve different purposes. OCMA-grade bentonite is a product grade with its own clause 19 and Table 18, while the base clay is a laboratory ingredient of the polyanionic cellulose test fluid and carries no grade of its own.
Test methods the material clauses use#
The material clauses measure properties such as viscosity, filtrate, coarse residue and density with laboratory instruments, so a lot is tested with field-type instruments under the conditions the specification sets. The test methods and their conditions are compared in the table below.
| Method | What it reports | Condition (edition) |
|---|---|---|
| Rotational viscometer (drilling fluid viscometer test) | Dial readings and YP/PV of a test suspension | Addendum 1 (OCMA clause) and 18th edition (2010) text |
| Low-pressure filter press (API filter press) | Filtrate volume | 100 +/- 5 psi (700 +/- 30 kPa) |
| Wet sieve | Residue above 75 µm | Addendum 1 text |
| Le Chatelier flask | Density of barite and hematite | 90 degF (32 +/- 0.5 degC) bath, 18th edition (2010) text |
| Chemical analysis of barite | Impurities | API RP 13K, 4th edition (2022) |
The test methods name no dose of any material in a field mud and no dial-reading limit; those belong to each material clause and its material page.
How Does API Spec 13A Relate to ISO 13500?#
ISO 13500:2008 is the ISO counterpart of API Spec 13A, a third edition published on 2008-10-22 by ISO/TC 67/SC 3 with 93 pages. ISO Open Data lists it at stage 90.20, under systematic review (snapshot 2026-10-21), together with Cor 1:2009 and Amd 1:2010 "Barite 4,1".
The two earlier ISO editions, ISO 13500:1998 and ISO 13500:2006, are withdrawn. The 2008 edition added PAC-LV, PAC-HV and xanthan gum as clauses 17 to 19, which matches the 18th-edition clause list. CEN adopted the text as EN ISO 13500:2008 with AC:2009 and A1:2010, and a national ISO member catalogue listed ISO 13500:2008 as valid with no replacement on 2026-10-27.
The status chain of ISO 13500 is listed in the table below.
| Date | ISO document | Status |
|---|---|---|
| 1998-07-16 | ISO 13500:1998 (1st edition) | Withdrawn |
| 2006-02-09 | ISO 13500:2006 (2nd edition) | Withdrawn |
| 2008-10-22 | ISO 13500:2008 (3rd edition, 93 pages) | Current, stage 90.20 (under systematic review) |
| 2009-06-26 | ISO 13500:2008/Cor 1:2009 | Stage 60.60 (published) |
| 2010-11-22 | ISO 13500:2008/Amd 1:2010 "Barite 4,1" (11 pages) | Stage 60.60 (published) |
| CEN | EN ISO 13500:2008 with AC:2009 and A1:2010 | European adoption |
ISO Open Data snapshot of 2026-10-21, read 2026-10-27.
Why ISO 13500 and API Spec 13A are cited separately#
ISO 13500 and API Spec 13A carry different dates (ISO 13500 2008 with amendments to 2010, API Spec 13A 2019 with amendments to 2024), so this reference cites each by edition and calls ISO 13500 the ISO counterpart. API revised API Spec 13A in 2019 without a matching ISO edition, so a clause number or grade label in one document is checked in the other before it goes into a contract.
Is There a Free API Spec 13A PDF?#
No: API sells the full API Spec 13A text, while Addendum 1, Addendum 2 and Errata 1 are free of charge as PDF files on the API Monogram advisories page. The full API Spec 13A and ISO 13500 texts are sold through API and authorized standards stores.
The three amendments sit on the API Monogram advisories page, which listed no further API Spec 13A notice after Errata 1 when checked on 2026-10-27. PDF copies found in search results are mostly older texts, such as the 18th edition (2010) or a 16th-edition purchasing guide, so their values and clause numbers can differ from the current edition. A buyer or laboratory therefore cites the edition it works to, with its amendments, in every order and test report.
Pending Revisions of API Spec 13A and ISO 13500#
API lists a 20th edition of API Spec 13A as in development with no date (API Standards Plan, checked 2026-10-27), and ISO 13500:2008 is under systematic review with no revision published (ISO Open Data, snapshot 2026-10-21). Until either document changes, the 19th edition with its three amendments and ISO 13500:2008 with Cor 1:2009 and Amd 1:2010 remain the texts to cite.
How Does API Spec 13A Fit Among Drilling Fluid Standards?#
API Spec 13A specifies the materials that go into a drilling fluid, while the API Recommended Practices of the 13 series test the fluid made from them in the field and the laboratory.
A mud engineer meets both kinds of document: the material grade on the sack comes from API Spec 13A, while the mud weight, rheology and filtrate in the daily report come from the Recommended Practices among the drilling fluid standards. Testing of heavy brines and completion fluids under their own API and ISO documents is a separate field, not covered here.
Related testing standards#
API RP 13B-1 covers field testing of water-based fluids in its 6th edition (2026), and API RP 13I covers laboratory testing of drilling fluid materials and fluids in its 9th edition (2020). The related testing standards and their relation to API Spec 13A are compared in the table below.
| Standard | Edition | Relation to API Spec 13A |
|---|---|---|
| API RP 13B-1 | 6th edition (2026) | Field testing of water-based fluids made with API 13A materials |
| API RP 13B-2 | 6th edition (2023) with Addendum 1 (2025) | Field testing of nonaqueous fluids |
| API RP 13I | 9th edition (2020) with Addendum 1 (2023) | Laboratory testing of drilling fluid materials and fluids |
| ISO 10414-1 | Stage 90.93 (confirmed) | Normative reference of the 18th edition (2010) text |
What API Spec 13A does not set#
API Spec 13A sets no heavy-metal limit and no purchasing terms, so four limits and documents come from other instruments, listed below.
- Mercury and cadmium in stock barite: on the US Outer Continental Shelf, 40 CFR 435.13 limits the barite used to formulate a discharged fluid to 1 mg/kg mercury and 3 mg/kg cadmium on a dry-weight basis, under the US offshore discharge rules.
- Speciality, single-source and limited-source products: outside the scope of API Spec 13A (18th edition (2010) text).
- Quote documents such as grade, certificate of analysis and packaging: buyers specify drilling fluid additives in a quote.
- Supplier quotes for an API grade: readers can request quotes from drilling fluid additive suppliers.