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;                                                                                                                                                                                                                                                                
| |    |                                                                                                                                                                                                                                                                                                                                                      
| | 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;                                                      
| |    |                                                                                                                                                                                                                                                                                                                                                      
| | 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:
| |    |                                                                                                                                                                                                                                                                                                                                                       |                                                                                                                                                                                                                                                                                                                                                                                                        
| |    |                                                                                                                                                                                                                                                                                                                                                       | (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) Evaluate
  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                                                                                                         
| |    |                                                                                                                                                                                                                                                                                                                                                       |                                                                                                                                                                                                                                                                                                                                                                                                        
| |    |                                                                                                                                                                                                                                                                                                                                                       | (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
| |    |                                                                                                                                                                                                                                                                                                                                                       |                                                                                                                                                                                                                                                                                                                                                                                                        
| | 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: | May 6, 2008                                           
|------ | ------------------------------------------------------
|       |                                                       
|/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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