Fourth quarter US GAAP net income increased to $13.8 million, or $0.34 per diluted share, versus net income of $3.9 million, or $0.09 per diluted share, in the prior year period. Net income in the 2012 fourth quarter includes a non-cash net tax benefit of $10.9 million or $0.27 per diluted share primarily related to the release of valuation allowance against U.S. net deferred tax assets as well as $1.3 million from the unanticipated sale of ZEV Credits,which were partially offset by approximately $1.0 million in previously anticipated costs associated with Hurricane Sandy, including vehicle damages and increased operating costs, and $0.8 million in costs associated with the Merger Agreement. The release of the valuation allowance is based on the projected ability of Zipcar to utilize the deferred tax assets to offset future taxable income in the U.S. Net income in the fourth quarter of 2011 included a gain on the sale of ZEV Credits of $2.5 million. US GAAP net income for the full year 2012 was $14.7 million, or $0.35 per diluted share, compared to a loss of $7.2 million, or ($0.24) per share, in 2011.
Adjusted EBITDA for the 2012 fourth quarter increased to $7.3 million, which excludes the effect of the aforementioned release of the valuation allowance, gains on the sale of ZEV Credits and costs associated with Hurricane Sandy, compared to $5.9 million in the prior year period. For the full year 2012, adjusted EBITDA was $17.2 million compared to $10.9 million in 2011. Adjusted EBITDA for all comparable periods exclude other costs and income as stated in the reconciliation of adjusted EBITDA below.
Change to Quarterly Conference Call PolicyDue to the previously announced Merger Agreement, Zipcar will not host a conference call in conjunction with today's release of its fourth quarter and full-year results and will not be updating prior financial guidance or providing financial guidance for future periods.