UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

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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 sections 240.13d-1(e), 240.13d-1(f) or 140.13d-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 section 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 the disclosures provided in a prior cover page.

The information required in 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).

Potential persons who are to respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB control number.

Check the Appropriate Box if a Member of a Group (See Instructions)

Source of Funds (See Instructions)

Check if Disclosure of Legal Proceedings Is Required Pursuant to Items 2(d) or 2(e) ____

Citizenship or Place of Organization

California

Number of

Beneficially

Owned by

Each Reporting

Person With

7. Sole Voting Power 0

8. Shared Voting Power 15,752,500

9. Sole Dispositive Power 0

10. Shared Dispositive Power 15,752,500

11.

Aggregate Amount Beneficially Owned by Each Reporting Person

15,752,500

12.

Check if the Aggregate Amount in Row (11) Excludes Certain Shares (See

13.

Percent of Class Represented by Amount in Row (11)

9.3%

14.

Type of Reporting Person (See Instructions)

CO, HC

Check the Appropriate Box if a Member of a Group (See Instructions)

Source of Funds (See Instructions)

Check if Disclosure of Legal Proceedings Is Required Pursuant to Items 2(d) or 2(e) ____

Citizenship or Place of Organization

California

Number of

Beneficially

Owned by

Each Reporting

Person With

7. Sole Voting Power 0

8. Shared Voting Power 15,752,500

9. Sole Dispositive Power 0

10. Shared Dispositive Power 15,752,500

11.

Aggregate Amount Beneficially Owned by Each Reporting Person

15,752,500

12.

Check if the Aggregate Amount in Row (11) Excludes Certain Shares (See

13.

Percent of Class Represented by Amount in Row (11)

9.3%

14.

Type of Reporting Person (See Instructions)

IA, OO

Check the Appropriate Box if a Member of a Group (See Instructions)

Source of Funds (See Instructions)

Check if Disclosure of Legal Proceedings Is Required Pursuant to Items 2(d) or 2(e) ____

Citizenship or Place of Organization

_______

Number of

Beneficially

Owned by

Each Reporting

Person With

7. Sole Voting Power 50,000

8. Shared Voting Power 15,752,500

9. Sole Dispositive Power 50,000

10. Shared Dispositive Power 15,752,500

11.

Aggregate Amount Beneficially Owned by Each Reporting Person

15,802,500

12.

Check if the Aggregate Amount in Row (11) Excludes Certain Shares (See

13.

Percent of Class Represented by Amount in Row (11)

9.3%

14.

Type of Reporting Person (See Instructions)

IN, HC

Check the Appropriate Box if a Member of a Group (See Instructions)

Source of Funds (See Instructions)

Check if Disclosure of Legal Proceedings Is Required Pursuant to Items 2(d) or 2(e) ____

Citizenship or Place of Organization

U.S.A.

Number of

Beneficially

Owned by

Each Reporting

Person With

7. Sole Voting Power 0

8. Shared Voting Power 15,752,500

9. Sole Dispositive Power 0

10. Shared Dispositive Power 15,752,500

11.

Aggregate Amount Beneficially Owned by Each Reporting Person

15,752,500

12.

Check if the Aggregate Amount in Row (11) Excludes Certain Shares (See

13.

Percent of Class Represented by Amount in Row (11)

9.3%

14.

Type of Reporting Person (See Instructions)

IN, HC

This statement relates to the Common Shares (the "Stock") of Canadian Superior Energy Inc. (the "Issuer"). The principal executive office of the Issuer is located at Suite 3200, 500 - 4th Avenue SW, Calgary, Alberta, Canada, T2P 2V6.

The persons filing this statement and the persons enumerated in Instruction C of Schedule 13D and, where applicable, their respective places of organization, general partners, directors, executive officers and controlling persons, and the information regarding them, are as follows:

(a)

William Leland Edwards, Palo Alto Investors, LLC ("PAI LLC"), Palo Alto Investors ("PAI Corp") and Anthony Joonkyoo Yun, MD (collectively, the "Filers").

(c)

Present principal occupation or employment or the Filers and the name, principal business and address of any corporation or other organization in which such employment is conducted:

PAI LLC is an investment adviser registered with the Securities and Exchange Commission and is the general partner of, and investment adviser to, investment limited partnerships. The sole manager of PAI LLC is PAI Corp. Mr. Edwards is the controlling shareholder of PAI Corp and the controlling owner of PAI LLC. Mr. Yun is the president of PAI Corp and PAI LLC.

(d)

During the last five years, none of the Filers has been convicted in a criminal proceeding (excluding traffic violations or similar misdemeanors).

(e)

During the last five years, none of the Filers was a party to a civil proceeding of a judicial or administrative body of competent jurisdiction and as a result of such proceeding was or is subject to a judgment, decree or final order enjoining future violations of, or prohibiting or mandating activities subject to, federal or state securities laws or finding any violation with respect to such laws.

Purchaser	Source of Funds	Amount
PAI LLC	Funds Under Management	$32,303,231

The Filers acquired the Stock for investment purposes. On September 29, 2008, Greg Noval sent a letter to Palo Alto Investors on behalf of the Issuer's Board of Directors responding to a letter from Palo Alto Investors sent earlier in the day, and Palo Alto Investors sent a further response to the Board. A copy of that correspondence is incorporated by reference herein as Exhibit B. On November 5, 2008, PAI LLC sent a letter to the Board, a copy of which is incorporated by reference herein as Exhibit F. On February 11, 2009, PAI LLC sent a letter to the Board questioning the timing and strategy of the Issuer’s proposed monetization of part of its Block 5(c) assets in Trinidad and Tobago (the “February 11 Letter”). On February 12, 2009, PAI LLC issued a press release including the text of the February 11 Letter and requesting additional disclosure by the Issuer with regard to its financial position and the status of that project and requesting that the Issuer hold a public conference call to update shareholders. A copy of that press release is incorporated by reference herein as Exhibit G. On February 17, 2009, PAI LLC delivered to the Issuer a requisition for a special meeting of the Issuer’s shareholders for the purpose, among other things, of removing all of the directors on the Issuer’s board of directors and replacing such directors with PAI LLC’s nominees (the “Requisition”). Also on February 17, 2009, PAI LLC issued a press release announcing that it had requisitioned a special meeting of the Issuer’s shareholders for that purpose (the “February 17 Press Release”). Once a record date and meeting date for the shareholders meeting have been established, a dissident proxy circular will be mailed to shareholders of record by PAI LLC. The dissident proxy circular will provide details regarding each of PAI LLC's nominees to the Issuer's Board of Directors. Shareholders are urged to carefully read the dissident proxy circular and other documents when they are available. A copy of the Requisition is incorporated by reference herein as Exhibit H, and a copy of the February 17 Press Release is incorporated by reference herein as Exhibit I. On March 10, 2009, PAI LLC sent a letter to the Board (the “March 10 Letter”) noting that no response had been provided to its February 11, 2009 inquiry regarding the Issuer’s proposed monetization of part of its Block 5(c) assets in Trinidad and Tobago and requesting a meeting with the full Board to discuss strategic and financing alternatives to monetizing the Block 5(c) assets. A copy of the March 10 Letter is incorporated herein by reference as Exhibit J. On March 16, 2009, PAI LLC sent a letter (the “March 16 Letter”) to the Board. The March 16 Letter was sent in response to an electronic mail message sent by Greg Noval (the “March 10 Noval E-mail”) to PAI LLC responding to the March 10 Letter sent earlier in the day on March 10, 2009, and in response to a letter from C. Alexander Squires, a director and chair of the Audit Committee of the Issuer's Board of Directors (the “March 12 Board Letter”) to PAI LLC on behalf of the Issuer's Board of Directors responding to the March 10 Letter. The March 16 Letter attaches a draft term sheet that PAI LLC believes is reflective of the type of transaction that is available to the Issuer from third parties if the Issuer would be willing to enter into discussions with such third parties (the “Draft Term Sheet”) and which could serve as a potential alternative to the Issuer’s proposed sale of part of its Block 5(c) assets in Trinidad and Tobago. The March 16 Letter also attaches copies of the March 10 Noval E-Mail and the March 12 Board Letter. The foregoing descriptions of the March 16 Letter, the Draft Term Sheet, the March 10 Noval Email and the March 12 Board Letter are each qualified in their entirety by reference to the terms of such documents. A copy of the March 16 Letter is incorporated herein by reference as Exhibit K. On April 1, 2009, PAI LLC issued, via press release, an open letter (the “April 1 Letter”) to the Board of Directors and Shareholders of the Issuer describing PAI LLC’s view of the failings, misconduct and inadequate corporate governance of the current Board and again demanding that the Board be reconstituted to include truly independent Directors with relevant international oil and gas expertise. The foregoing description of the April 1 Letter is qualified in its entirety by reference to the terms of such document. A copy of the April 1 Letter is incorporated herein by reference as Exhibit L. On April 2, 2009, Mr. V. Phil Lalonde of Brownlee LLP wrote PAI LLC on behalf of Greg Noval,

asserting, among other things, that the April 1 Letter contains statements that defame Mr. Noval. On April 3, 2009, Canadian counsel to PAI LLC, Blake, Cassels & Graydon LLP, sent a letter to Mr. Lalonde responding to his April 2, 2009 letter. The foregoing description of the April 3 Letter is qualified in its entirety by reference to the terms of such document. A copy of the April 3 Letter is attached hereto as Exhibit M.

In pursuing their investment purposes, the Filers may from time to time further purchase, hold, vote, trade, dispose of, engage in option, swap or other derivative securities transactions with respect to or otherwise deal in the Stock at times, and in such manner, as they deem advisable to benefit from changes in the Stock's market price, changes in the Issuer's operations, business strategy or prospects, or from sale or merger of the Issuer. To evaluate such alternatives, the Filers routinely will monitor the Issuer's operations, prospects, business development, management, competitive and strategic matters, capital structure and prevailing market conditions, as well as alternative investment opportunities, the Filers' liquidity requirements and other investment considerations. Consistent with their investment research methods and evaluation criteria, the Filers may discuss such matters with the Issuer's management, Board of Directors, other shareholders, industry analysts, existing or potential strategic partners or competitors, investment and financing professionals, sources of credit and other investors. Such factors and discussions may affect materially, and result in, the Filers' modifying their ownership of the Stock, exchanging information with the Issuer pursuant to appropriate confidentiality or similar agreements, proposing changes in the Issuer's operations, governance or capitalization, or in proposing or taking one or more of the actions described in paragraphs (a) through (j) of Item 4 of Schedule 13D. The Filers may reconsider and change their plans or proposals relating to the Stock at any time.

(a), (b), (d) Each Filer's beneficial ownership of the Stock on the date of this report is reflected on that Filer's cover page. PAI LLC is an investment adviser with the power to invest in, vote and dispose of the Stock on behalf of its clients. Its clients have the right to receive or the power to direct the receipt of dividends from, or the proceeds from the sale of, the Stock. No client individually holds more than 5% of the outstanding Stock. Mr. Edwards is the controlling shareholder of PAI Corp, which is the sole manager of PAI LLC, and is the controlling owner of PAI LLC. Mr. Yun is the president of PAI Corp and PAI LLC. The Filers are filing this Schedule 13D jointly, but not as members of a group, and each of them expressly disclaims membership in a group. Each Filer disclaims beneficial ownership of the Stock except to the extent of that Filer's pecuniary interest therein.

Item 6. Contracts, Arrangement, Understandings or Relationships with Respect to Securities of the Issuer

PAI LLC is the general partner of investment partnerships pursuant to agreements of limited partnership that grant to PAI LLC the authority, among other things, to invest the funds of such investment partnerships in the Stock, to vote and dispose of the Stock and to file this statement on behalf of such investment partnerships. Pursuant to such agreements, PAI LLC is entitled to allocations based on assets under management and realized and unrealized gains.

In addition, 750,000 shares of the Stock are represented by warrants, the form of which is incorporated by reference herein as Exhibit C. In addition, those warrants are governed by and subject to the terms of a Securities Purchase Agreement and Registration Rights Agreement, the forms of which are incorporated by reference herein as Exhibits D and E.

Exhibit B

Correspondence dated September 29, 2008 between the Issuer's Board of Directors and Palo Alto Investors incorporated by reference to the Filers’ initial Schedule 13D and Amendment No. 1 thereto both filed September 30, 2008

Exhibit C

Form of Warrant to Purchase Shares of Common Stock incorporated by reference to the Issuer's Form F-3 filed September 26, 2008

Exhibit D

Form of Securities Purchase Agreement incorporated by reference to the Issuer's Form F-3 filed September 26, 2008

Exhibit E

Form of Registration Rights Agreement incorporated by reference to the Issuer's Form F-3 filed September 26, 2008

Exhibit F

Letter dated November 5, 2008 from PAI LLC to the Issuer's Board of Directors incorporated by reference to Amendment No. 2 to this Schedule 13D filed November 6, 2008

Exhibit G

Press Release by PAI LLC dated February 12, 2009 including the text of the February 11 Letter incorporated by reference to Amendment No. 3 to this Schedule 13D filed February 12, 2009

Exhibit H

Requisition delivered by PAI LLC to the Issuer dated February 17, 2009 incorporated by reference to Amendment No. 4 to this Schedule 13D filed February 17, 2009

Exhibit I

Press Release by PAI LLC dated February 17, 2009 incorporated by reference to Amendment No. 4 to this Schedule 13D filed February 17, 2009

Exhibit J

Letter dated March 10, 2009 from PAI LLC to the Issuer's Board of Directors incorporated by reference to Amendment No. 5 to this Schedule 13D filed March 10, 2009

Exhibit K

Letter dated March 16, 2009 from PAI LLC to the Issuer's Board of Directors (attaching the Draft Term Sheet, and the electronic mail message dated March 10, 2009 from Greg Noval to PAI LLC and Letter dated March 12, 2009 from C. Alexander Squires on behalf of the Issuer's Board of Directors to PAI LLC) incorporated by reference to Amendment No. 6 to this Schedule 13D filed March 16, 2009.

Exhibit L

Open Letter dated April 1, 2009 from PAI LLC to the Issuer's Board of Directors and Shareholders incorporated by reference to Amendment No. 7 to this Schedule 13D filed April 1, 2009

Exhibit M

Letter dated April 3, 2009 from Blake, Cassels & Graydon LLP to Mr. V. Phil Lalonde of Brownlee LLP

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

PALO ALTO INVESTORS

By: /s/ Mark Shamia
Mark Shamia, Chief Operating Officer

PALO ALTO INVESTORS, LLC

By: /s/ Mark Shamia
Mark Shamia, Chief Operating Officer

/s/ Anthony Joonkyoo Yun

Anthony Joonkyoo Yun, MD

/s/ William Leland Edwards

William Leland Edwards

The undersigned agree to file jointly with the Securities and Exchange Commission (the "SEC") any and all statements on Schedule 13D or Schedule 13G (and any amendments or supplements thereto) required under section 13(d) of the Securities Exchange Act of 1934, as amended, in connection with purchases and sales by the undersigned of the securities of any issuer until such time as the undersigned file with the SEC a statement terminating this Agreement Regarding Joint Filing of Statement on Schedule 13D or 13G. For that purpose, the undersigned hereby constitute and appoint Palo Alto Investors, LLC, a California limited liability company, as their true and lawful agent and attorney-in-fact, with full power and authority for and on behalf of the undersigned to prepare or cause to be prepared, sign, file with the SEC and furnish to any other person all certificates, instruments, agreements and documents necessary to comply with section 13(d) and section 16(a) of the Securities Exchange Act of 1934, as amended, in connection with said purchases and sales, and to do and perform every act necessary and proper to be done incident to the exercise of the foregoing power, as fully as the undersigned might or could do if personally present, until such time as the undersigned file with the SEC a statement terminating this Agreement Regarding Joint Filing of Statement on Schedule 13D or 13G.

PALO ALTO INVESTORS

By: /S/ Mark Shamia, Chief Operating Officer

PALO ALTO INVESTORS, LLC

By: /S/ Mark Shamia, Chief Operating Officer

/S/ Anthony Joonkyoo Yun, MD

/S/ William Leland Edwards

We have your letter of April 2, 2009 sent to our client Palo Alto Investors, LLC and David J. Anderson. Our client disagrees that the Open Letter is defamatory. It was written to the Board and shareholders to set out Palo Alto’s concerns respecting events which have harmed the Company and their investment in it. The letter contains factually correct information which is of interest to investors, and potential investors, in Canadian Superior Energy.

Palo Alto’s actions have always been to seek to preserve the value of their investment in the shares of Canadian Superior, both on their own behalf and on behalf of all shareholders.

It is unfortunate the Mr Noval has reacted to the Open Letter by threatening a lawsuit on his own behalf rather than focussing on the issues facing the Company and working towards improving the situation of Canadian Superior Energy. Our client is pleased to hear, in that regard, that a fully independent committee of the Board has now been established (Canadian Superior press release – April 3, 2009) with a mandate to review all alternatives and proposals available to the Company. Palo Alto was also pleased to see that the Committee has retained an independent financial advisor and is in the process of obtaining independent counsel.

Palo Alto looks forward to working with the Committee and its advisors in the execution of the Committee’s mandate.