Chad Utrup
Analyst · Robert Kosowsky
Thanks Merv. Our revenues, as you saw for this past quarter, were $225.8 million, which is an increase of $67.8 million or 43% from the fourth quarter of 2010. This increase is primarily the result of our global OEM truck market revenues, which increased nearly $47 million or 71% from the fourth quarter of 2010.
Our global OEM construction revenues also saw a sharp increase of approximately $12 million or 28% from the same period last year, while our other end markets collectively increased approximately $9 million or 18% from the prior year quarter. Operating income was $16.1 million or 7.1% of revenues, which is an improvement of approximately $10.7 million over the prior year period.
Sequentially, revenues were up approximately $8.9 million from the third quarter of 2011 with an operating income increase of $2.5 million or 28% contribution margin. With start-up cost related to our Saltillo and Beijing expansions beginning to subside along with strong focus on cost and margin improvement, we are extremely pleased with our performance this quarter and the contribution on incremental revenues.
Depreciation and amortization was $3.1 million and capital spending was $6.9 million for the quarter, and our interest expense was generally in line with what we discussed on our last quarter conference call. Tax provision for the quarter was slightly lower than expected and is primarily related to tax expense for our foreign operations, offset by changes in valuation allowances for our U.S. based entities.
Looking forward to 2012, our estimate for tax provision at this time is approximately 20% of pre-tax income, and we will continue to monitor the status of our valuation allowances as we progress through the year. You will notice that, we did record approximately $15,000 attributable to our non-controlling interest. This is related to the new joint -- India joint venture with Hema Engineering and represents their 10% interest in the JV for the period.
From a fully diluted EPS standpoint, the quarter came in at $0.36, which we are again proud to report as our highest diluted EPS levels since the fourth quarter of 2006. As of the end of this past quarter, we had a cash balance of approximately $88 million, this cash balance combined with our ABL revolver capacity, means we have approximately $125 million of liquidity immediately available as we continue to look at strategic opportunities.
As we look to 2012, while we are not providing guidance, our estimates for North American Class 8 units is in the range of 280,000 to 290,000 units, and we currently expect our global OEM construction market to remain flat to up 5% from what we saw in the last half of 2011. In addition, we would like to remind you of certain timing events within our cost structure, which include annual wage adjustments and certain customer price concessions beginning January 1 of 2012.
While this can impact our sequential contribution margin when comparing Q4 of 2011 to Q1 of 2012, we expect our operating income or EBITDA contribution margin on the change in revenues for the full year 2011 to 2012 to remain in the 20% to 25% range excluding any 1x investment expenses such as Mexico, Beijing or India, which we saw last year as an example.
To recap, this quarter marks our highest revenue, operating income and diluted earnings per share since the fourth quarter of 2006. As Merv mentioned, this is also our 11th consecutive quarter of operating income improvements when excluding impairment and restructuring charges. This is something we are extremely proud of and we look forward to continuing our focus on operating and financial improvements as well as our long-term growth strategy as we move forward.
And with that, we'll open the call up for any questions.