$19.6 million in the 2006 period.
Earnings per share were $0.17 compared to $0.20 for the fourth quarter of 2006. Operating income during the fourth quarter of 2007 was negatively impacted approximately $4.6 million or $0.03 per share due to an increase in fuel cost, net of fuel surcharge revenue.
For the year ended Dec. 31, operating revenues increased 3.5 percent to $591.9 million from $571.9 million during the same period in 2006. Net income decreased 12.6 percent to $76.2 million from $87.2 million in the 2006 period. Earnings per share were $0.78 compared with $0.89 for the 2006 period. Operating income for the year was negatively impacted by a $8 million decrease in gains on disposal of property and equipment. In addition, operating income for the year was negatively impacted approximately $10.5 million or $0.07 per share due to an increase in fuel cost, net of fuel surcharge revenue.
For the quarter, Heartland Express, Inc. posted an operating ratio (operating expenses as a percentage of operating revenues) of 83.9 percent and a 10.9 percent net margin (net income as a percentage of operating revenues). The company reported an operating ratio of 81.3 percent and a 12.9 percent net margin for the year. The company ended the year with cash, cash equivalents, and short-term investments of $196.6 million, a $134.7 million decrease from the $331.3 million reported on Dec. 31, 2006, due to the special $196.5 million dividend paid in 2007. The company's balance sheet continues to be debt-free.
The average age of the company's tractor fleet was 2.1 years at the end of 2007, with the entire tractor fleet consisting of 2005 or newer model year International tractors. The average age of the company's trailer fleet was 3.8 years with the entire trailer fleet consisting of 2002 or newer model year Wabash trailers.