One Gas Inc — Current Report (Form 8-K)

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

PURSUANT TO SECTION 13 OR 15(d)

OF THE SECURITIES EXCHANGE ACT OF 1934

(Date of report) August 13, 2026

(Date of earliest event reported) August 11, 2026

ONE Gas, Inc.

(Exact name of registrant as specified in its charter)

15 East Fifth Street

Tulsa, OK 74103

(Address of principal executive offices) (Zip code)

(918) 947-7000

(Registrant’s telephone number, including area code)

Not Applicable

(Former name or former address, if changed since last report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

Securities registered pursuant to Section 12(b) of the Act:

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (17 CFR §230.405) or Rule 12b-2 of the Securities Exchange Act of 1934 (17 CFR §240.12b-2).

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. ☐

Underwriting Agreement

On August 11, 2026, ONE Gas, Inc. (“ONE Gas”) entered into an underwriting agreement (the “Underwriting Agreement”) with BofA Securities, Inc., RBC Capital Markets, LLC and Truist Securities, Inc., as representatives of the underwriters named therein (the “Underwriters”), with respect to the issuance and sale by ONE Gas of $375,000,000 aggregate principal amount of its 5.45% Senior Notes due 2036 (the “Notes”).

The Underwriting Agreement contains customary representations, warranties and agreements by ONE Gas and customary conditions to closing, indemnification obligations of ONE Gas, on the one hand, and the Underwriters, on the other hand, including for liabilities under the Securities Act of 1933, as amended (the “Securities Act”), obligations of the parties and termination provisions.

The foregoing description of the Underwriting Agreement is qualified in its entirety by reference to such Underwriting Agreement, a copy of which is filed herewith as Exhibit 1.1 and is incorporated herein by reference.

Supplemental Indentures and Notes

On August 13, 2026, ONE Gas completed the underwritten public offering (the “Offering”) of the Notes. The Offering of the Notes was registered under the Securities Act pursuant to ONE Gas’ shelf registration statement on Form S-3 which became automatically effective upon filing with Securities and Exchange Commission on February 23, 2026 (File No. 333-293655). ONE Gas anticipates using the net proceeds from the Offering to repay our $250 million unsecured term loan and amounts outstanding under its commercial paper program and for general corporate purposes.

The terms of the Notes are governed by the Indenture, dated as of August 13, 2026 (the “Base Indenture”), between ONE Gas and U.S. Bank Trust Company, National Association, as trustee (the “Trustee”), as supplemented by the Supplemental Indenture No. 1 (the “First Supplemental Indenture”) dated as of August 13, 2026.

Each of the Base Indenture, the First Supplemental Indenture and the form of the Notes is filed herewith as Exhibit 4.1, 4.2, and 4.3, respectively, and is incorporated herein by reference.

Affiliations

The Underwriters and their respective affiliates are full service financial institutions engaged in various activities, which may include securities trading, commercial and investment banking, financial advisory, investment management, principal investment, hedging, financing and brokerage activities. The Underwriters and their respective affiliates have provided in the past and may provide from time to time in the future certain commercial banking, financial advisory, investment banking and other services for ONE Gas or its subsidiaries for which they will receive customary fees. Affiliates of certain of the Underwriters are also lenders under ONE Gas’ credit facility, term loan and dealers under ONE Gas’ $1.5 billion commercial paper program.

The Trustee and certain of its affiliates have from time to time performed, and may in the future perform, various financial advisory, commercial and investment banking services for ONE Gas for which they received or will receive customary fees and expenses. The Trustee is a lender under ONE Gas’ credit facility.

The information included in Item 1.01 with respect to the Notes and the Indenture above is incorporated herein by reference.

(d) Exhibits

SIGNATURE

Pursuant to the requirements of the Securities Exchange Act of 1934, as amended, the registrant has duly caused this report to be signed on its behalf by the undersigned, hereunto duly authorized.