Electric fuel and purchased power expenses decreased approximately $19.5 million during the 2012 twelve month period when compared to the 2011 period, reflecting reduced demand as a result of the mild weather and lower customer counts discussed above.
In summary, electric segment gross margin increased approximately $10.8 million during the twelve months ended September 30, 2012, compared to the 2011 period, primarily due to the increased customer rates.
Other regulated operating expenses increased approximately $10.7 million due primarily to increased pension and healthcare expenses, professional services fees, Iatan 2 and Plum Point generating station operations expenses, and transmission operations expenses. Maintenance expenses were higher by approximately $2.0 million in the 2012 twelve month period. Increases in production maintenance expenses were partially offset by decreases in transmission maintenance expenses and maintenance expenses associated with our Iatan generating station.
Depreciation expense decreased approximately $6.7 million during the 2012 period. Increased depreciation due to higher levels of plant in service and the ending of deferred depreciation related to construction accounting was more than offset by a reduction of approximately $10.2 million in regulatory amortization which ended June 15, 2011 with the implementation of new customer rates from our most recent Missouri rate case. Other taxes increased approximately $0.6 million as a result of the higher levels of plant in service and increased municipal franchise taxes.
Electric segment net income increased approximately $1.5 million during the 2012 twelve month period when compared to the 2011 period.
Twelve Months Ended Gas Segment Results
Gross margin for the gas segment decreased $2.9 million during the 2012 twelve month period compared to the same period in 2011, as the mild weather experienced during the fourth quarter of 2011 and first quarter of 2012 resulted in decreased customer usage. Other regulated operating and maintenance expenses were relatively unchanged during the 2012 period. Depreciation increased about $0.1 million and other taxes were lower by $0.3 million when compared to the 2011 period. Gas segment net income decreased approximately $1.6 million during the 2012 twelve month period compared to the 2011 period.