SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

Schedule 13G
(Rule 13d-102)

INFORMATION TO BE INCLUDED IN STATEMENTS FILED PURSUANT TO RULES 13d-1 (b), (c) AND (d)
AND AMENDMENTS THERETO FILED PURSUANT TO 13d-2 (b)

(Amendment No. 1)*

Tenable Holdings, Inc.

(Name of Issuer)

Common Stock, $0.01 par value

(Title of Class of Securities)

88025T102

(CUSIP Number)

December 31, 2019

(Date of Event Which Requires Filing of this Statement)

Check the appropriate box to designate the rule pursuant to which this Schedule is filed:

¨       Rule 13d-1(b)

¨       Rule 13d-1(c)

x       Rule 13d-1(d)

*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).

(Continued on following pages)

CUSIP NO.  88025T102 13 G

1	NAME OF REPORTING SS OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON Accel XI L.P. (“A11”)
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP* (a)     ¨    (b)     x
3	SEC USE ONLY
4	CITIZENSHIP OR PLACE OF ORGANIZATION Delaware

NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH	5	SOLE VOTING POWER 2,182,696 shares, all of which are directly owned by A11. Accel XI Associates L.L.C. (“A11A”), the general partner of A11, may be deemed to have sole power to vote these shares.
	6	SHARED VOTING POWER See response to row 5.
	7	SOLE DISPOSITIVE POWER 2,182,696 shares, all of which are directly owned by A11. A11A, the general partner of A11, may be deemed to have sole power to dispose of these shares.
	8	SHARED DISPOSITIVE POWER See response to row 7.

9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON	2,182,696
10	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES*	¨
11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9	2.2%(1)
12	TYPE OF REPORTING PERSON*	PN

(1) Based on 98,187,608 shares of common stock outstanding as of November 8, 2019, as reported by the Issuer in its Quarterly Report on Form 10-Q for the quarter ended September 30, 2019, filed with the Securities and Exchange Commission on November 14, 2019 (the “Form 10-Q”).

CUSIP NO.  88025T102 13 G

1	NAME OF REPORTING SS OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON Accel XI Strategic Partners L.P. (“A11SP”)
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP* (a)     ¨    (b)     x
3	SEC USE ONLY
4	CITIZENSHIP OR PLACE OF ORGANIZATION Delaware

NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH	5	SOLE VOTING POWER 163,992 shares, all of which are directly owned by A11SP. A11A, the general partner of A11SP, may be deemed to have sole power to vote these shares.
	6	SHARED VOTING POWER See response to row 5.
	7	SOLE DISPOSITIVE POWER 163,992 shares, all of which are directly owned by A11SP. A11A, the general partner of A11SP, may be deemed to have sole power to dispose of these shares.
	8	SHARED DISPOSITIVE POWER See response to row 7.

9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON	163,922
10	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES*	¨
11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9	0.2%(1)
12	TYPE OF REPORTING PERSON*	PN

(1) Based on 98,187,608 shares of common stock outstanding as of November 8, 2019, as reported by the Issuer in Form 10-Q.

CUSIP NO.  88025T102 13 G

1	NAME OF REPORTING PERSONS I.R.S. IDENTIFICATION NO. OF ABOVE PERSON Accel XI Associates L.L.C.
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (a)     ¨    (b)     x
3	SEC USE ONLY
4	CITIZENSHIP OR PLACE OF ORGANIZATION Delaware

NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH	5	SOLE VOTING POWER 2,346,688 shares, of which 2,182,696 are directly owned by A11 and 163,992 are directly owned by A11SP. A11A, the general partner of A11 and A11SP, may be deemed to have sole power to vote these shares.
	6	SHARED VOTING POWER See response to row 5.
	7	SOLE DISPOSITIVE POWER 2,346,688 shares, of which 2,182,696 are directly owned by A11 and 163,992 are directly owned by A11SP. A11A, the general partner of A11 and A11SP, may be deemed to have sole power to dispose of these shares.
	8	SHARED DISPOSITIVE POWER See response to row 7.

9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON	2,346,688
10	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES	¨
11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9	2.4%
12	TYPE OF REPORTING PERSON	OO

(1) Based on 98,187,608 shares of common stock outstanding as of November 8, 2019, as reported by the Issuer in Form 10-Q.

CUSIP NO.  88025T102 13 G

1	NAME OF REPORTING SS OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON Accel Investors 2013 L.L.C. (“AI13”)
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP* (a)     ¨    (b)     x
3	SEC USE ONLY
4	CITIZENSHIP OR PLACE OF ORGANIZATION Delaware

NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH	5	SOLE VOTING POWER 231,806 shares, all of which are directly owned by AI13.
	6	SHARED VOTING POWER See response to row 5.
	7	SOLE DISPOSITIVE POWER 231,806 shares, all of which are directly owned by AI13.
	8	SHARED DISPOSITIVE POWER See response to row 7.

9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON	231,806
10	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES*	¨
11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9	0.2%(1)
12	TYPE OF REPORTING PERSON*	OO

(1) Based on 98,187,608 shares of common stock outstanding as of November 8, 2019, as reported by the Issuer in Form 10-Q.

CUSIP NO.  88025T102 13 G

1	NAME OF REPORTING SS OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON Accel Growth Fund II L.P.
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP* (a)     ¨    (b)     x
3	SEC USE ONLY
4	CITIZENSHIP OR PLACE OF ORGANIZATION Delaware

NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH	5	SOLE VOTING POWER 0
	6	SHARED VOTING POWER 0
	7	SOLE DISPOSITIVE POWER 0
	8	SHARED DISPOSITIVE POWER 0

9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON	0
10	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES*	¨
11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9	0.0%(1)
12	TYPE OF REPORTING PERSON*	PN

(1) Based on 98,187,608 shares of common stock outstanding as of November 8, 2019, as reported by the Issuer in Form 10-Q.

CUSIP NO.  88025T102 13 G

1	NAME OF REPORTING SS OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON Accel Growth Fund II Strategic Partners L.P.
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP* (a)     ¨    (b)     x
3	SEC USE ONLY
4	CITIZENSHIP OR PLACE OF ORGANIZATION Delaware

NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH	5	SOLE VOTING POWER 0
	6	SHARED VOTING POWER 0
	7	SOLE DISPOSITIVE POWER 0
	8	SHARED DISPOSITIVE POWER 0

9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON	0
10	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES*	¨
11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9	0.0%(1)
12	TYPE OF REPORTING PERSON*	PN

(1) Based on 98,187,608 shares of common stock outstanding as of November 8, 2019, as reported by the Issuer in Form 10-Q.

CUSIP NO.  88025T102 13 G

1	NAME OF REPORTING SS OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON Accel Growth Fund II Associates L.L.C.
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP* (a)     ¨    (b)     x
3	SEC USE ONLY
4	CITIZENSHIP OR PLACE OF ORGANIZATION Delaware

NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH	5	SOLE VOTING POWER 0
	6	SHARED VOTING POWER 0
	7	SOLE DISPOSITIVE POWER 0
	8	SHARED DISPOSITIVE POWER 0

9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON	0
10	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES*	¨
11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9	0.0%(1)
12	TYPE OF REPORTING PERSON*	OO

(1) Based on 98,187,608 shares of common stock outstanding as of November 8, 2019, as reported by the Issuer in Form 10-Q.

CUSIP NO.  88025T102 13 G

1	NAME OF REPORTING SS OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON Accel Growth Fund Investors 2012 L.L.C.
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP* (a)     ¨    (b)     x
3	SEC USE ONLY
4	CITIZENSHIP OR PLACE OF ORGANIZATION Delaware

NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH	5	SOLE VOTING POWER 0
	6	SHARED VOTING POWER 0
	7	SOLE DISPOSITIVE POWER 0
	8	SHARED DISPOSITIVE POWER 0

9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON	0
10	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES*	¨
11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9	0.0%(1)
12	TYPE OF REPORTING PERSON*	OO

(1) Based on 98,187,608 shares of common stock outstanding as of November 8, 2019, as reported by the Issuer in Form 10-Q.

CUSIP NO.  88025T102 13 G

1	NAME OF REPORTING SS OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON Accel Growth Fund III L.P. (“AGF3”)
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP* (a)     ¨    (b)     x
3	SEC USE ONLY
4	CITIZENSHIP OR PLACE OF ORGANIZATION Delaware

NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH	5	SOLE VOTING POWER 4,326,710 shares, all of which are owned by AGF3. Accel Growth Fund III Associates L.L.C. (“AGF3A”), the general partner of AGF3, may be deemed to have sole power to vote these shares.
	6	SHARED VOTING POWER See response to row 5.
	7	SOLE DISPOSITIVE POWER 4,326,710 shares, all of which are owned by AGF3. AGF3A, the general partner of AGF3, may be deemed to have sole power to dispose of these shares.
	8	SHARED DISPOSITIVE POWER See response to row 7.

9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH  REPORTING PERSON	4,326,710
10	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES*	¨
11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9	4.4%(1)
12	TYPE OF REPORTING PERSON*	PN

(1) Based on 98,187,608 shares of common stock outstanding as of November 8, 2019, as reported by the Issuer in Form 10-Q.

CUSIP NO.  88025T102 13 G

1	NAME OF REPORTING SS OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON Accel Growth Fund III Strategic Partners L.P. (“AGF3SP”)
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP* (a)     ¨    (b)     x
3	SEC USE ONLY
4	CITIZENSHIP OR PLACE OF ORGANIZATION Delaware

NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH	5	SOLE VOTING POWER 204,267 shares, all of which are directly owned by AGF3SP. AGF3A, the general partner of AGF3SP, may be deemed to have sole power to vote these shares.
	6	SHARED VOTING POWER See response to row 5.
	7	SOLE DISPOSITIVE POWER 204,267 shares, all of which are directly owned by AGF3SP. AGF3A, the general partner of AGF3SP, may be deemed to have sole power to dispose of these shares.
	8	SHARED DISPOSITIVE POWER See response to row 7.

9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON	204,267
10	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES*	¨
11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9	0.2%(1)
12	TYPE OF REPORTING PERSON*	PN

(1) Based on 98,187,608 shares of common stock outstanding as of November 8, 2019, as reported by the Issuer in Form 10-Q.

CUSIP NO.  88025T102 13 G

1	NAME OF REPORTING SS OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON Accel Growth Fund III Associates L.L.C.
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP* (a)     ¨    (b)     x
3	SEC USE ONLY
4	CITIZENSHIP OR PLACE OF ORGANIZATION Delaware

NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH	5	SOLE VOTING POWER 4,530,977 shares, of which 4,326,710 are directly owned by AGF3 and 204,267 are directly owned by AGF3SP. AGF3A, the general partner of AGF3 and AGF3SP, may be deemed to have sole power to vote these shares.
	6	SHARED VOTING POWER See response to row 5.
	7	SOLE DISPOSITIVE POWER 4,530,977 shares, of which 4,326,710 are directly owned by AGF3 and 204,267 are directly owned by AGF3SP. AGF3A, the general partner of AGF3 and AGF3SP, may be deemed to have sole power to dispose of these shares.
	8	SHARED DISPOSITIVE POWER See response to row 7.

9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON	4,530,977
10	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES*	¨
11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9	4.6%(1)
12	TYPE OF REPORTING PERSON*	OO

(1) Based on 98,187,608 shares of common stock outstanding as of November 8, 2019, as reported by the Issuer in Form 10-Q.

CUSIP NO.  88025T102 13 G

1	NAME OF REPORTING SS OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON Accel Growth Fund Investors 2014 L.L.C. (“AGFI14”)
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP* (a)     ¨    (b)     x
3	SEC USE ONLY
4	CITIZENSHIP OR PLACE OF ORGANIZATION Delaware

NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH	5	SOLE VOTING POWER 286,648 shares, all of which are directly owned by AGFI14.
	6	SHARED VOTING POWER See response to row 5.
	7	SOLE DISPOSITIVE POWER 286,648 shares, all of which are directly owned by AGFI14.
	8	SHARED DISPOSITIVE POWER See response to row 7.

9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON	286,648
10	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES*	¨
11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9	0.3%(1)
12	TYPE OF REPORTING PERSON*	OO

(1) Based on 98,187,608 shares of common stock outstanding as of November 8, 2019, as reported by the Issuer in Form 10-Q.

CUSIP NO.  88025T102 13 G

This Amendment No. 1 (“Amendment No. 1”) amends and supplements the Schedule 13G initially filed with the United States Securities and Exchange Commission on February 13, 2019 (the “Original Schedule 13G”) by the Reporting Persons. The “Reporting Persons” are collectively, Accel XI L.P. (“A11”), Accel XI Strategic Partners L.P. (“A11SP”), Accel XI Associates L.L.C. (“A11A”), Accel Investors 2013 L.L.C. (“AI13”), Accel Growth Fund II L.P. (“AGF2”), Accel Growth Fund II Strategic Partners L.P. (“AGF2SP”), Accel Growth Fund II Associates L.L.C., a Delaware limited liability company (“AGF2A”), Accel Growth Fund Investors 2012 L.L.C. (“AGFI12”), Accel Growth Fund III L.P. (“AGF3”), Accel Growth Fund III Strategic Partners L.P. (“AGF3SP”), Accel Growth Fund III Associates L.L.C. (“AGF3A”), and Accel Growth Fund Investors 2014 L.L.C. (“AGFI14”). Only those items that are hereby reported are amended; all other items reported in the Original Schedule 13G remain unchanged. Information given in response to each item shall be deemed incorporated by reference in all other items, as applicable. Capitalized terms not defined in this Amendment No. 1 have the meanings ascribed to them in the Original Schedule 13G.

ITEM 4. OWNERSHIP

The following information with respect to the ownership of the Common Stock of the issuer by the persons filing this Statement is provided as of December 31, 2019.

(a) Amount beneficially owned:

See Row 9 of cover page for each Reporting Person.

(b) Percent of Class:

See Row 11 of cover page for each Reporting Person.

(c) Number of shares as to which such person has:

(i) Sole power to vote or to direct the vote:

See Row 5 of cover page for each Reporting Person.

(ii) Shared power to vote or to direct the vote:

See Row 6 of cover page for each Reporting Person.

(iii) Sole power to dispose or to direct the disposition of:

See Row 7 of cover page for each Reporting Person.

(iv) Shared power to dispose or to direct the disposition of:

See Row 8 of cover page for each Reporting Person.

ITEM 5. OWNERSHIP OF FIVE PERCENT OR LESS OF A CLASS

If this statement is being filed to report the fact that as of the date hereof the reporting person has ceased to be the beneficial owner of more than 5% of the class of securities, check the following: x

CUSIP NO.  88025T102 13 G

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.

Date: February 12, 2020

Entities:	Accel XI L.P.*
	Accel XI Strategic Partners L.P.*
	Accel XI Associates L.L.C.*
	Accel Investors 2013 L.L.C.*
	Accel Growth Fund II L.P.*
	Accel Growth Fund II Strategic Partners L.P.*
	Accel Growth Fund II Associates L.L.C.*
	Accel Growth Fund Investors 2012 L.L.C.*
	Accel Growth Fund III L.P.*
	Accel Growth Fund III Strategic Partners L.P.*
	Accel Growth Fund III Associates L.L.C.*
	Accel Growth Fund Investors 2014 L.L.C.*

By:	/s/ Tracy L. Sedlock
	Tracy L. Sedlock, Attorney-in-fact for
	the above-listed entities

* Signed pursuant to a Power of Attorney already on file with the appropriate agencies.