SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 13D

(Rule 13d-101)

INFORMATION TO BE INCLUDED IN STATEMENTS FILED PURSUANT TO § 240.13d-1(a)
AND AMENDMENTS THERETO FILED PURSUANT TO § 240.13d-2(a)

UNDER THE SECURITIES EXCHANGE ACT OF 1934

(Amendment No. 18)*

Oaktree Specialty Lending Corporation

(Name of Issuer)

Common Stock, par value $0.01 per share

(Title of Class of Securities)

67401P 108

(CUSIP Number)

Leonard M. Tannenbaum

525 Okeechobee Boulevard, Suite 1770

West Palm Beach, FL 33401

(203) 930-2139

(Name, Address and Telephone Number of Person Authorized to Receive Notices and Communications)

May 21, 2021

(Date of Event Which Requires Filing of this Statement)

If the filing person has previously filed a statement on Schedule 13G to report the acquisition that is the subject of this Schedule 13D, and is filing this schedule because of §§ 240.13d-1(e), 240.13d-1(f) or 240.13d-1(g), check the following

box. ¨

Note: Schedules filed in paper format shall include a signed original and five copies of the schedule, including all exhibits. See § 240.13d-7 for other parties to whom copies are to be sent.

*The remainder of this cover page shall be filled out for a reporting person’s initial filing on this form with respect to the subject class of securities, and for any subsequent amendment containing information which would alter disclosures provided in a prior cover page.

The information required on the remainder of this cover page shall not be deemed to be “filed” for the purpose of Section 18 of the Securities Exchange Act of 1934 (“Act”) or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes).

This Schedule 13D/A constitutes Amendment No. 18 to the Schedule 13D filed by Leonard M. Tannenbaum on December 31, 2015, as amended on January 29, 2016, February 24, 2016, March 29, 2016, September 12, 2016, December 21, 2016, March 7, 2017, March 10, 2017, March 27, 2017, July 17, 2017, October 4, 2017, October 25, 2017, April 12, 2019, July 9, 2019, December 20, 2019, January 30, 2020, December 15, 2020 and March 26, 2021. Except as amended herein, each such prior Schedule 13D, as previously amended, remains in effect. Capitalized terms used herein but not otherwise defined in this Amendment shall have the meaning ascribed to them in the reporting persons’ Schedules 13D as previously amended.

Item 5 is amended and restated as follows:

(a)-(b) The information set forth in rows 7 through 13 of the cover page to this Schedule 13D is incorporated by reference. The percentage set forth in row 13 is based on 180,360,662 Shares outstanding as of May 4, 2021, as reported in the Issuer’s Form 10-Q as filed on May 6, 2021. For purposes of Section 13 of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), Mr. Tannenbaum has shared voting and dispositive power with Oaktree over the following Shares: (i) 21,195,331 Shares held by Mr. Tannenbaum directly; (ii) 1,379,824 Shares held by the Leonard M. Tannenbaum Foundation, for which Mr. Tannenbaum serves as the President; and (iii) 1,332,773 Shares held directly by the Leonard M. Tannenbaum 2012 Trust for the benefit of certain members of Mr. Tannenbaum’s family for which Mr. Bernard D. Berman and Mr. James Castro-Blanco are Co-Trustees.

(c) Schedule A sets forth all transactions with respect to Shares effected during the past 60 days.

Schedule A

¹ Price per Share excludes commissions paid.

SIGNATURES

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

Dated: May 28, 2021