v2.4.0.6

Document and Entity Information	3 Months Ended
Document and Entity Information	Mar. 31, 2012	May 09, 2012
Document and Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2012
Entity Registrant Name	Ridgewood Energy M Fund LLC
Entity Central Index Key	0001302834
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2012
Document Fiscal Period Focus	Q1
Entity Filer Category	Smaller Reporting Company
Entity Common Stock, Shares Outstanding		535.6818

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Ridgewood Energy M Fund LLC 10-Q