All other revenue, which consists of technology products and services, information and user access fees, investment income and other revenue, decreased to $6.2 million, compared to $6.4 million for the fourth quarter of 2011.
Total expenses for the fourth quarter of 2012 increased 9.9% to $28.9 million, compared to $26.3 million for the fourth quarter of 2011. The increase in expenses during the fourth quarter of 2012 was primarily due to higher professional and consulting fees and employee compensation and benefits costs. Fourth quarter 2012 expenses included approximately $1.0 million of Xtrakter acquisition-related costs. Fourth quarter 2011 expenses included an accounts receivable allowance provision and minority investment write-off aggregating approximately $1.5 million.
The effective tax rate for the fourth quarter of 2012 was 4.9%, compared to 38.8% for the fourth quarter of 2011. Excluding the impact of the non-recurring favorable income tax adjustment, the effective tax rate for the fourth quarter was 36.3%.
Employee headcount as of December 31, 2012 was 240, compared to 232 as of December 31, 2011.Full Year 2012 Results Total revenues for the year ended December 31, 2012 increased 9.4% to a record $198.2 million, compared to $181.1 million for 2011. Pre-tax income was a record $86.7 million, compared to $78.7 million for 2011, an increase of 10.1%. Pre-tax margin was 43.7%, compared to 43.5% for 2011. Net income totaled $60.1 million, or $1.59 per share on a diluted basis, compared to $47.7 million, or $1.20 per share on a diluted basis, for 2011. Excluding the income tax adjustment, net income totaled $53.3 million, or $1.41 per share on a diluted basis. Commission revenue for the year ended December 31, 2012 increased 12.1% to $174.2 million, compared to $155.4 million for 2011. Variable transaction fees increased 25.3% to $114.9 million on total trading volume of $589.6 billion, compared to variable transaction fees of $91.7 million on total trading volume of $525.0 billion for 2011.