EBITDA for twelve months ended December 31, 2012 was $124.0 million, compared to $88.6 million in 2011. EBITDA for the current period, excluding Partnership level expenses and acquisition costs related to the Pasadena Facility, totaled $135.8 million. The East Dubuque Facility and the Pasadena Facility contributed $137.5 million and ($1.7) million in EBITDA, respectively, during the twelve months ended December 31, 2012. As part of purchase accounting adjustments related to the acquisition of Agrifos, the value of inventory was increased to fair value as of the closing date, which resulted in an approximately $3.4 million increase in the cost of product sold by the Pasadena Facility during the two-month period ended December 31, 2012. Further explanation of EBITDA, a non-GAAP financial measure, and a reconciliation of Rentech Nitrogen's EBITDA to net income have been included below in this press release.
Gross margins for the twelve months ended December 31, 2012 were 50%, compared to 43% last year. The increase in gross margins was primarily attributable to an increase in product pricing and lower natural gas costs. Average natural gas costs in cost of sales for the East Dubuque Facility were $3.59 per MMBtu for the twelve months ended December 31, 2012, compared to $4.76 per MMBtu for the prior year. Average ammonia and sulfur costs in cost of sales for the Pasadena Facility were $658 per ton and $154 per ton, respectively for the current period.
SG&A expenses were $18.4 million for the twelve months ended December 31, 2012, compared to $7.7 million for the prior year. The increase was primarily due to business development expenses of approximately $4.5 million, including approximately $4.1 million for the Agrifos acquisition. In addition, Rentech Nitrogen was a publicly traded limited partnership for twelve full months in 2012 as compared to 52 days in 2011, which resulted in increases in non-cash unit-based compensation of approximately $2.6 million, payroll costs of approximately $1.3 million, approximately $1.0 million in professional and other fees related to being a publicly-traded partnership, and $0.7 million of fees on the unused credit facility. Current period expenses also include $0.4 million in SG&A expenses at the Pasadena Facility. The increase in SG&A expenses was partially offset by a $0.7 million reduction in audit and tax fees due to additional audit and tax work in 2011 required for the IPO and change in fiscal year.