TRS-RenTelco, our electronic test equipment division, rental revenues for the quarter increased by $1.8 million, or 7% to $26.5 million from a year ago. Divisional income from operations increased by 24% from the third quarter of 2011 to $10.2 million. The significantly higher percentage increase in profitability as compared to rental revenues was primarily related to lower direct SG&A and equipment depreciation expenses, partially offset by higher laboratory costs, all as a percentage of rental revenues from a year ago. Our results for TRS-RenTelco continue to reflect its discipline in strategic focus, strong brand following, operational efficiencies and an exceptionally talented and tenured work force.
Adler Tank Rentals, our tank and box division, rental revenues increased by $0.8 million, or 5% to $16.9 million from a year ago. Divisional income from operations decreased by $1.9 million or 20% year over year to $7.6 million. The decrease in profitability was primarily due to lower utilization driving higher rental equipment depreciation as a percentage of rental revenues, and higher inventory center costs from a year ago. As a result of the ongoing reduction in dry natural gas production in the Northeast and markedly lower utilization of Adler’s 21,000 gallon tank fleet in the region, we moved a large number of units to other regions, primarily to fill order opportunities. The one-time costs to transport these tanks were a material portion of the increase in inventory center expenses compared to a year ago.
The higher depreciation expense as a percentage of rental revenues was the result of a significant increase in year over year rental equipment inventory to support a larger geographic footprint and new customer growth opportunities, and lower equipment utilization levels, primarily in the Northeast, from a year ago. Division-wide Adler rental equipment utilization declined to 69.4% at the end of the third quarter compared to 90.5% a year ago; however, utilization increased from 67.5% from the end of the second quarter 2012. We are building the Adler brand across the continental U.S. and it is essential that we have the right mix and depth of inventory on the ground in all of the markets in which we operate in order to respond to a variety of end market needs. In fact, Adler’s industry mix of rental revenues for the third quarter of 2012 compared to the same period in 2011 reflects fracking related rentals decreasing from approximately 35% to 19%, while overall rental revenues increased 5%.