our agreement with American Express, sales of non-jet fuel products to third parties by our oil refinery and maintenance sales to third parties by our MRO services business.

Operating Expense

 	

Salaries and Related Costs. The increase in salaries and related costs is primarily due to higher pilot and flight attendant block hours and pay rate increases implemented in both the first half of 2015 and December 2015. Base pay rates increased 14.5% for eligible merit, ground and flight attendant employees effective December 1, 2015.

Aircraft Fuel and Related Taxes. Including our regional carriers, fuel expense decreased $5.9 billion compared to the prior year due to a 43.5% decrease in the market price per gallon of fuel, an increase in Monroe's profitability and reduced hedge losses, partially offset by a 2.4% increase in consumption. The table below presents fuel expense, including our regional carriers.

Regional Carriers Expense. The reduction in regional carriers expense is primarily due to lower fuel cost from a decrease in the price per gallon of fuel, lower capacity and reduced maintenance expenses. During 2015, we removed t hirty 50-seat regional aircraft as part of our strategy to restructure our domestic fleet.

Contracted Services. The increase in contracted services expense predominantly related to costs associated with the 3.0% increase in capacity and additional temporary staffing.

Depreciation and Amortization. Depreciation and amortization expense increased year-over-year primarily due to investments in new A330-300, B-737-900ER and CRJ-900 aircraft and aircraft modifications that upgraded aircraft interiors and enhanced our product offering.

Landing Fees and Other Rents. Landing fees and other rents increased principally due to increased number of departures and higher rental rates.

Profit Sharing. The increase in profit sharing is driven by an increase in full year pre-tax income compared to the prior year. Our broad-based employee profit sharing program provides that, for each year in which we have an annual pre-tax profit, as defined by the terms of the program, we will pay a specified portion of that profit to employees. In determining the amount of profit sharing, the program defines profit as pre-tax profit adjusted for profit sharing and certain other items. For years prior to 2016, our profit sharing program paid 10% to employees for the first $2.5 billion of annual profit and 20% of annual profit above $2.5 billion.

Beginning with 2016 pre-tax profit (to be paid out in 2017), the profit sharing formula will be adjusted to pay 10% of annual pre-tax profit (as defined by the terms of the program) and, if we exceed our prior-year results, the program will pay 20% of the year-over-year increase in pre-tax profit to eligible employees. The profit sharing program for pilots remains unchanged and will continue in 2016 under its terms.

Passenger Service. Passenger service expense includes the costs for onboard food and beverage, cleaning and supplies. This expense increased year-over-year primarily due to costs associated with enhancements to our onboard product offering and the 3.3% increase in traffic.

Other. Other