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)) 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





(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:
            
            November
      9, 2009/s/
            
            KATHLEEN
      P. MCSHERRYName:
            
            Kathleen
      P. McSherryTitle:
            
            Executive
      Vice President and Chief Financial Officer(Principal
      Financial Officer)