UNITED STATES 
 SECURITIES AND EXCHANGE COMMISSION 
 Washington, D.C. 20549 
 
 SCHEDULE 13G 
 
 Under the Securities Exchange Act of 1934 
 (Amendment No. 5)*	

Semgroup Corporation
(Name of Issuer)	
 	
Common Stock – Class A
(Title of Class of Securities)	
 
81663A105
(CUSIP Number)
 	
December 31, 2017
(Date of Event which Requires Filing of this Statement)	

Check the appropriate box to designate the rule pursuant to which this Schedule is filed:	
 	
[	X	]  Rule 13d-1(b)	
[	 	]  Rule 13d-1(c)	
[	 	]  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 the 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).	

SCHEDULE 13G	
CUSIP No. 81663A105	
 	
 	1.	Names of Reporting Persons. 
  
Iridian Asset Management LLC
I.R.S. Identification Nos. of above persons (entities only).	
 	
 	2.	Check the Appropriate Box if a Member of a Group (See Instructions) 
 (a)  [X ]       (b)  [   ]	
 	
 	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 
 N/A	
	 	
	6.	Shared Voting Power 
 N/A	
	 	
	7.	Sole Dispositive Power 
 N/A	
	 	
	8.	Shared Dispositive Power 
 N/A	
 	
 	9.	Aggregate Amount Beneficially Owned by Each Reporting Person 
 N/A	
 	
 	10.	Check if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions)  [    ]	
 	
 	11.	Percent of Class Represented by Amount in Row (9)
N/A	
 	
 	12.	Type of Reporting Person
IA	
 	
2
 	
SCHEDULE 13G	
CUSIP No. 81663A105	
 	
 	1.	Names of Reporting Persons. 
  
David L. Cohen
I.R.S. Identification Nos. of above persons (entities only).	
 	
 	2.	Check the Appropriate Box if a Member of a Group (See Instructions) 
 (a)  [ X  ]       (b)  [   ]	
 	
 	3.	SEC USE ONLY	
 	
 	4.	Citizenship or Place of Organization
United States	
 	
Number of 
 Shares 
 Beneficially 
 Owned by 
 Each Reporting 
 Person With:	5.	Sole Voting Power 
 N/A	
	 	
	6.	Shared Voting Power 
 N/A	
	 	
	7.	Sole Dispositive Power 
 N/A	
	 	
	8.	Shared Dispositive Power 
 N/A	
 	
 	9.	Aggregate Amount Beneficially Owned by Each Reporting Person 
 N/A	
 	
 	10.	Check if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions)  [    ]	
 	
 	11.	Percent of Class Represented by Amount in Row (9)
N/A	
 	
 	12.	Type of Reporting Person
IN	
 	
3
 	
SCHEDULE 13G	
CUSIP No. 81663A105	
 	
 	1.	Names of Reporting Persons. 
  
Harold J. Levy
I.R.S. Identification Nos. of above persons (entities only).	
 	
 	2.	Check the Appropriate Box if a Member of a Group (See Instructions) 
 (a)  [X]       (b)  [   ]	
 	
 	3.	SEC USE ONLY	
 	
 	4.	Citizenship or Place of Organization
United States	
 	
Number of 
 Shares 
 Beneficially 
 Owned by 
 Each Reporting 
 Person With:	5.	Sole Voting Power 
 N/A	
	 	
	6.	Shared Voting Power 
 N/A	
	 	
	7.	Sole Dispositive Power 
 N/A	
	 	
	8.	Shared Dispositive Power 
 N/A	
 	
 	9.	Aggregate Amount Beneficially Owned by Each Reporting Person 
 N/A	
 	
 	10.	Check if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions)  [    ]	
 	
 	11.	Percent of Class Represented by Amount in Row (9)
N/A	
 	
 	12.	Type of Reporting Person
IN	
 	
4
 	
This Schedule amends in its entirety the Schedule filed for the period ended December 31, 2016.

Item 1.	
 	(a)	Name of Issuer 
 
 Semgroup Corporation
 	
 	(b)	Address of Issuer's Principal Executive Offices
Two Warren Place, 6120 S. Yale Avenue, Suite 700, Tulsa, OK 74136-4216	
 	
Item 2.	
 	(a)	Name of Person Filing
This  Statement is being filed by and on behalf of Iridian Asset  Management LLC ("Iridian"), David L. Cohen ("Cohen") and Harold J. Levy ("Levy") (collectively, the "Reporting Persons").
Iridian is majority owned by Arovid Associates LLC, a Delaware limited liability company owned and controlled by the following: 12.5% by Cohen, 12.5% by Levy, 37.5% by LLMD LLC, a Delaware limited liability company, and 37.5% by ALHERO LLC, a Delaware limited liability company. LLMD LLC is owned 1% by Cohen, and 99% by a family trust controlled by Cohen. ALHERO LLC is owned 1% by Levy and 99% by a family trust controlled by Levy.
 	
 	(b)	Address of Principal Business Office or, if none, Residence 
 
 The principal business address of the Reporting Persons is 276 Post Road West, Westport, CT 06880-4704.	
 	(c)	Citizenship or Place of Organization 
 
 Iridian is a Delaware limited liability company. Cohen and Levy are US citizens.
 	
 	(d)	Title of Class of Securities 
 
 Common Stock, $.01 par value – Class A.
 	
 	(e)	CUSIP Number 
 
 81663A105

Item 3.	If this statement is filed pursuant to §§240.13d-1(b) or 240.13d-2(b) or (c), check whether the person filing is a:	
 	(a)	[   ]	Broker or dealer registered under section 15 of the Act (15 U.S.C. 78o).	
 	(b)	[   ]	Bank as defined in section 3(a)(6) of the Act (15 U.S.C. 78c).	
 	(c)	[   ]	Insurance company as defined in section 3(a)(19) of the Act (15 U.S.C. 78c).	
 	(d)	[   ]	Investment company registered under section 8 of the Investment Company Act of 1940 (15 U.S.C 80a-8).	
 	(e)	[  ]	An investment adviser in accordance with §240.13d-1(b)(1)(ii)(E);	
 	(f)	[   ]	An employee benefit plan or endowment fund in accordance with §240.13d-1(b)(1)(ii)(F);	
 	(g)	[   ]	A parent holding company or control person in accordance with § 240.13d-1(b)(1)(ii)(G);	
 	(h)	[   ]	A savings associations as defined in Section 3(b) of the Federal Deposit Insurance Act (12 U.S.C. 1813);	
 	(i)	[   ]	A church plan that is excluded from the definition of an investment company under section 3(c)(14) of the Investment Company Act of 1940 (15 U.S.C. 80a-3);	
 	(j)	[ x]	Group, in accordance with §240.13d-1(b)(1)(ii)(J).	
 	
Item 4.	Ownership.	
 	(a) and (b)	Amount beneficially owned and Percent of Class:

 Not applicable.	
 	 	 	
 	(c)	Power to vote or dispose.
Not applicable.	
 	
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 five percent of the class of securities, check the following [  X  ].

Item 6.	Ownership of More than Five Percent on Behalf of Another Person	
Not Applicable	
 	
Item 7.	Identification and Classification of the Subsidiary Which Acquired the Security Being Reported on By the Parent Holding Company	
 
Not Applicable.	
 	
Item 8.	Identification and Classification of Members of the Group	
Iridian is an investment adviser registered under Section 203 of the Investment Advisers Act of 1940, and its principal business is managing a number of accounts containing securities over which Iridian has voting and dispositive power.
Each of Messrs. Cohen and Levy has a controlling interest in Iridian, and serves as Co-Chief Executive Officer and Co-Chief Investment Officer of Iridian.	
 	
Item 9.	Notice of Dissolution of Group	
 
Not Applicable

 	
Item 10.	Certification	
By  signing  below the  undersigned  certifies  that,  to the best of its or his knowledge  and belief,  the  securities  referred to above were acquired and are held in the  ordinary  course of business and were not acquired and are not held for the  purpose of and do not have the effect of changing  or  influencing  the control of the issuer of the  securities  and were not acquired and are not held in connection with or as a participant in any transaction having such purpose or effect.	
 	
SIGNATURE	
After reasonable inquiry and to the best of its or his knowledge and belief, we certify that the information set forth in this statement is true, complete and correct.	
 	
Date:   February 6, 2018	
 	IRIDIAN ASSET MANAGEMENT LLC
 	
 	By:	/s/ Jeffrey M. Elliott
_________________________
      Jeffrey M. Elliott	
 	Title:	   Executive Vice President	
 	
 	David L. Cohen
 	
 	By:	/s/ Jeffrey M. Elliott
_________________________
      Jeffrey M. Elliott	
 	Title:	   Agent 	
 	
 	Harold J. Levy
 	
 	By:	/s/ Jeffrey M. Elliott
__________________________
      Jeffrey M. Elliott	
 	Title:	   Agent