For the second quarter of 2012, our operating revenues increased by $4.5 million or 4.1% to $114.3 million. The main driver of this increase continues to be our contracted services segment, American States Utility Services, or ASUS. ASUS' revenue increased by $3.1 million to $25.1 million compared to the same period last year, primarily due to increased construction activity and favorable changes in cost estimates for water and wastewater pipeline replacement project at the Fort Bragg military base.
Water and electric utility revenue at Golden State Water increased by $1.4 million due to rate increases approved by the California Public Utilities Commission, effective January 1, 2012. 2012 is the final year of the current rate case cycle for both our water and electric utility business segments. Typically rate increases are the lowest during the last year of the rate cycle.
Our water electric supply costs were $26.7 million accounting for 31.7% of total operating expenses for the second quarter of '12. As you know, any changes in purchased water, power purchased for pumping, pump taxes for the water utility segment as compared to the adopted supply costs, are covered by Modified Cost Balancing Account. The electric utility segment also has a full cost balancing account to track the changes in purchased power and transmission-related costs. Other operation expenses remained constant as compared to the same period last year. Increases in conservation-related expenses, water treatment costs and employee-related costs at the water segment were offset by a lower precontract cost incurred at ASUS.