Increases at Tunnel Ridge and Onton also contributed to record coal production of 9.0 million tons in the 2012 Quarter, an increase of 17.7% compared to the 2011 Quarter. As expected, the increase in coal production and sales tons contributed to higher operating expenses in the 2012 Quarter, which increased 14.9% to $338.6 million.
Outside coal purchases decreased $15.4 million to $4.4 million in the 2012 Quarter compared to the 2011 Quarter, primarily as a result of reduced purchases of brokerage coal. Depreciation, depletion and amortization increased $19.5 million to $59.8 million in the 2012 Quarter compared to the 2011 Quarter, primarily as a result of the start-up of longwall production at the Tunnel Ridge mine, the addition of the Onton mine and capital expenditures related to infrastructure improvements at various other operations.
Comparative financial results for the 2012 Quarter continued to be impacted by anticipated losses related to ARLP's investments in White Oak Resources LLC ("White Oak") and the development of its Mine No.1. Our preferred equity investment in White Oak requires ARLP to record substantially all of White Oak’s income and losses until we achieve our contractual preferred return. As a result, net equity in loss of affiliates in the 2012 Quarter primarily reflects the pass through of approximately $3.0 million of losses related to White Oak’s mine development activities.
Nine Months Ended September 30, 2012 Compared to Nine Months Ended September 30, 2011For the nine months ended September 30, 2012 (the “2012 Period”), production increases at the River View, Warrior and Tunnel Ridge mines and the acquisition of the Onton mine in April 2012 led to record production and sales volumes as tons produced climbed 9.8% and tons sold increased 6.9%, compared to the nine months ended September 30, 2011 (the “2011 Period”). Higher coal sales volumes and increased average coal sales prices, which rose $1.04 per ton sold, combined to drive 2012 Period revenues to a record $1.5 billion, an increase of 8.5% compared to the 2011 Period. As discussed above, these increases were offset by reduced metallurgical coal sales, higher operating costs and depreciation, depletion and amortization, the Pontiki asset impairment charge, and losses related to our investments in White Oak. As a result, compared to the 2011 Period, net income for the 2012 Period fell 19.7% to $238.9 million, or $4.25 per basic and diluted limited partner unit, while Adjusted EBITDA declined 1.8% to $433.5 million.