Exhibit 31.2

CERTIFICATION

I, Kathleen P.
McSherry, certify that:

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| | 1. | I have
 reviewed this Annual Report on Form 10-K 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;                                                                                   
| |    |                                                                                                                                                                                                                                                                                                                                                                                                  
| | 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 Rule s 13a  15(f) and 15d 
 15(f)) for the registrant and have:                                                
| |    |                                                                                                                                                                                                                                                                                                                                                                                                  
| |    | (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;          
| |    |                                                                                                                                                                                                                                                                                                                                                                                                  
| |    | (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;                 
| |    |                                                                                                                                                                                                                                                                                                                                                                                                  
| |    | (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):                                                                                           
| |    |                                                                                                                                                                                                                                                                                                                                                                                                  
| |    | (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                                                                                                                 
| |    |                                                                                                                                                                                                                                                                                                                                                                                                  
| |    | (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.                                                                                                                                                                                                                 

|       |  |                                                       | 
|------ |  | ----------------------------------------------------- | 
|Dated: |  | March 12,
 2009                                       | 
|       |  |                                                       | 
|/s/    |  | KATHLEEN P.
 McSHERRY                                 | 
|       |  |                                                       | 
|Name:  |  | Kathleen P.
 McSherry                                 | 
|       |  |                                                       | 
|Title: |  | Executive
 Vice President and Chief Financial Officer | 
|       |  | (Principal
 Financial and Accounting Officer)         | 

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