January 2011: $3.08 February 2011: $3.48 March 2011: $3.57 April 2011: $3.88 May 2011: $3.91 June 2011: $3.65 July 2011: $3.70 August 2011: $3.60 September 2011: $3.66 October 2011: $3.46 November 2011: $3.37 December 2011: $3.23 January 2012: $3.44 February 2012: $3.72 March 2012: $3.93 Source: Consumer Reports