Exhibit
31.2





CERTIFICATION





I,
Kathleen P. McSherry, certify that:




1.
              I
      have reviewed this Annual Report on Form 10-K 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)  
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





(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:
            March
      22, 2010/s/
            KATHLEEN
      P. MCSHERRYName:
            Kathleen
      P. McSherryTitle:
            Executive
      Vice President and Chief Financial Officer(Principal
      Financial and Accounting Officer)