ACS Citation Style: In-Text Citations and Reference List Format

ACS citation style is the referencing system published by the American Chemical Society for chemistry journals, lab reports, and coursework. It gives writers three options for in-text citations, superscript numbers, numbers in parentheses, or an author-date format, paired with a matching reference list at the end of the paper. This guide covers each in-text option, the reference list rules for the source types students cite most often, and the mistakes that quietly cost points on a chemistry paper.

What Is ACS Citation Style?

ACS style was developed by the American Chemical Society to give chemistry authors, students, and researchers a consistent way to cite journal articles, books, and data sources. It is documented in full in The ACS Style Guide and is the default citation style for most ACS-published journals, as well as many undergraduate and graduate chemistry courses.

Unlike APA or MLA, ACS style does not lock writers into one in-text citation format. A journal, instructor, or department can choose superscript numbers, parenthetical numbers, or an author-date system, so the first step on any ACS paper is confirming which variant your instructor or target journal expects.

When to Use ACS Style

Use ACS style whenever you submit to an ACS-published journal, such as the Journal of the American Chemical Society or Analytical Chemistry, or whenever a chemistry course explicitly requires it. Many chemistry departments also default to ACS style for lab reports even outside a formal journal submission, since it matches the format students will use later when publishing research.

ACS In-Text Citation Formats

ACS recognizes three in-text citation methods. Pick one and use it consistently throughout the paper, mixing methods within the same document is one of the most common ACS citation mistakes.

The three ACS in-text citation methods

Method	Example	Typical use
Superscript numbers	Oscillation in the reaction was reported previously.3	Most common default for lab reports and journal submissions
Numbers in parentheses	Oscillation in the reaction was reported previously (3).	Preferred when superscripts are hard to format, such as in plain-text drafts
Author-date	Oscillation in the reaction was reported previously (Finnegan et al., 2004).	Chosen when the audience needs the author and year visible in the sentence

With numbered systems, sources are numbered in the order they first appear in the text, and that number stays fixed for every later mention of the same source. For two authors, list both surnames joined by “and”. For three or more authors, give the first author’s surname followed by “et al.” A closer breakdown of these in-text rules is available from West Virginia University’s ACS citation guide.

Which In-Text Method Should You Use?

If your assignment or target journal does not specify a method, use superscript numbers. It is the ACS default, it keeps sentences uncluttered in dense chemistry text, and most journal templates and reference managers are already configured to output it automatically.

How to Format an ACS Reference List

The reference list appears at the end of the paper, titled “References.” A few rules apply across every source type:

1. Order entries by citation number if you used a numbered in-text system, or alphabetically by author surname if you used author-date.
2. List up to 10 authors, separated by semicolons, with initials after each surname (e.g., Lehman, J. W.; Rudolph, M. G.).
3. Italicize journal titles and book titles.
4. Bold the publication year.
5. Include a DOI or accessed date for any source consulted online.

Journal articles no longer strictly require abbreviated journal titles in current ACS practice, but abbreviations following the CAS Source Index (CASSI) are still accepted and common in published chemistry literature. See our guide to citing journals for source-specific examples beyond the ACS format.

ACS Reference Examples by Source Type

Each source type follows a slightly different reference pattern in ACS style, and picking the wrong one is a common mistake. The table below covers the entries students cite most often, journal articles, books, book chapters, magazine and newspaper articles, and websites, so you can match your source to the right format without a database search.

ACS reference list formats by source type

Source type	Format & example
Journal article (print)	Author. Title of article. Journal Abbreviation Year, Volume, page range.
Journal article (online)	Author. Title of article. Journal Abbreviation [Online] Year, Volume, page range. URL (accessed Month Day, Year).
Book (without editor)	Author. Book Title, Edition; Publisher: Place, Year; page range.
Book chapter (edited book)	Author. Chapter Title. In Book Title; Editor, Ed.; Publisher: Place, Year; page range.
Magazine or newspaper article	Author. Title of Article. Magazine or Newspaper Title, Complete Date, page range. See our magazine citation guide or newspaper citation guide for the general (non-ACS) version of this format.
Website	Author (if any). Title of Site. URL (accessed Month Day, Year).

If you retrieved an article through a library database rather than the publisher’s own site, name the database provider before the URL. When you can’t find a DOI at all, search the publisher’s website directly rather than citing the database’s internal link, since database URLs often expire once your library access ends.

Common ACS Citation Mistakes to Avoid

Most ACS citation errors come from mixing conventions between styles or between the three in-text options, and graders notice inconsistency faster than they notice a single wrong format.

Other frequent mistakes include using commas instead of semicolons between multiple authors, forgetting to italicize the journal or book title, and leaving out the accessed date on an online source that has no DOI. A less obvious one: giving a data set or spectral chart its own reference entry without naming the specific figure or entry number, which makes the citation impossible for a reader to verify.

ACS Style vs. Other Citation Styles

ACS’s author-date variant is structurally close to Chicago author-date, which is why students who already know Chicago often find that option the easiest ACS variant to adopt. If your course allows a choice of style, or you need to cite the same source list in a paper for a non-chemistry class, these related guides cover the other formats:

• Chicago author-date citation generator
• How to cite a journal or magazine article
• How to cite a book
• How to cite a website

For a full comparison of citation styles used across academic writing, visit the EssayReply citation hub, or build a reference automatically with the EssayReply citation generator.

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