Exhibit 31.2

CERTIFICATION

I, Kathleen P. McSherry,
certify that:

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)) 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) 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

(c) 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 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: |  | November 2, 2007                                                                                   
|       |  |                                                                                                    
|/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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