EXHIBIT
31.2

CERTIFICATION

I,
Kathleen P. McSherry, certify that:

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| | 1. | I
 have reviewed this Quarterly Report on Form 10-Q of Ridgewood Energy O Fund,
 LLC;                                                                                                                                                                                                                                                           
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| | 2. | Based
 on my knowledge, this report does not contain any untrue statement of a
 material fact or omit to state a material fact necessary to make the
 statements made, in light of the circumstances under which such statements
 were made, not misleading with respect to the period covered by this report;                                  
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| | 3. | Based
 on my knowledge, the financial statements, and other financial information
 included in this report, fairly present in all material respects the
 financial condition, results of operations and cash flows of the registrant
 as of, and for, the periods presented in this report;                                                     
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| | 4. | The
 registrants other certifying officer(s) and I are responsible for
 establishing and maintaining disclosure controls and procedures (as defined
 in Exchange Act Rules 13a-15(e) and 15d-15(e)) and internal control over
 financial reporting (as defined in Exchange Act Rules 13a  15(f) and 15d 
 15(f)) for the registrant and have:

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| |  |  | (a)
 Designed such disclosure controls and procedures, or caused such disclosure
 controls and procedures to be designed under our supervision, to ensure that
 material information relating to the registrant, including its consolidated
 subsidiaries, is made known to us by others within those entities,
 particularly during the period in which this report is being prepared;         
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| |  |  | (b)
 Designed such internal control over financial reporting, or caused such
 internal control over financial reporting to be designed under our
 supervision, to provide reasonable assurance regarding the reliability of
 financial reporting and the preparation of financial statements for external
 purposes in accordance with generally accepted accounting principles;                
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| |  |  | (c)
 Evaluated the effectiveness of the registrants disclosure controls and
 procedures and presented in this report our conclusions about the
 effectiveness of the disclosure controls and procedures, as of the end of the
 period covered by this report based on such evaluation; and                                                                                                     
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| |  |  | (d)
 Disclosed in this report any change in the registrants internal control over
 financial reporting that occurred during the registrants most recent fiscal
 quarter (the registrants fourth fiscal quarter in the case of an annual
 report) that has materially affected, or is reasonably likely to materially
 affect, the registrants internal control over financial reporting; and

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| | 5. | The
 registrants other certifying officer(s) and I have disclosed, based on our
 most recent evaluation of internal control over financial reporting, to the
 registrants auditors and the audit committee of the registrants board of
 directors (or persons performing the equivalent functions):

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| |  |  | (a)
 All significant deficiencies and material weaknesses in the design or
 operation of internal control over financial reporting which are reasonably
 likely to adversely affect the registrants ability to record, process,
 summarize and report financial information; and
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| |  |  | (b)
 Any fraud, whether or not material, that involves management or other
 employees who have a significant role in the registrants internal control
 over financial reporting.                                                                                                

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|------ |  | ----------------------------------------------------- | 
|Dated: |  | April 28, 2009                                        | 
|       |  |                                                       | 
|/s/    |  | KATHLEEN P. McSHERRY                                  | 
|       |  |                                                       | 
|Name:  |  | Kathleen P. McSherry                                  | 
|       |  |                                                       | 
|Title: |  | Executive Vice President
 and Chief Financial Officer | 
|       |  | (Principal Financial
 Officer)                        | 

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