Refinery services Segment Margin decreased 2% for the fourth quarter and full year of 2012 over the comparable 2011 periods primarily due to the timing of NaHS sales to South American customers. In late 2011, we experienced a high volume of sales to these customers. Sales volumes to customers in South America can fluctuate due to scheduling of shipments. Also impacting the full year of 2012 results were longer than anticipated refinery turnarounds (in the first half of 2012) at some of our largest refinery service locations, which resulted in increased costs as a result of processing at less efficient locations to ensure uninterrupted supplies of NaHS to our customers.
Supply and logistics Segment Margin for the fourth quarter and full year of 2012 increased 70% and 55%, respectively, over the comparable 2011 periods. The primary factors for Segment Margin increasing were the contribution of the black oil barge transportation assets that we acquired in August 2011 and February 2012 and increased volumes handled by our expanded trucking, rail and barge fleets. Our total volumes of crude oil and refined products increased 48% and 32% for the fourth quarter and full year of 2012, respectively, primarily as a result of these expansions.
Other Components of Available Cash before Reserves
Corporate general and administrative expenses included in the calculation of Available Cash before Reserves increased by $4.1 million and $8.7 million for the fourth quarter and full year of 2012, respectively, over comparable 2011 results, primarily due to increased salaries and benefits associated with additional personnel to support our growth and increased equity compensation expense driven by a higher common unit price.Interest costs for the fourth quarter of 2012 increased $2.5 million from the fourth quarter of 2011 and increased $8.9 million on a year-over-year comparison primarily as a result of increased borrowings for acquisitions and other growth projects. Capitalized interest costs attributable to our growth capital expenditures and investments in the SEKCO pipeline joint venture partially offset the increase in interest expense, resulting in a net increase in interest expense included in the calculation of Available Cash before Reserves of $1.1 million and $5.2 million for the fourth quarter and full year of 2012, respectively, over the comparable 2011 periods.