2015 second quarter financial results represent our 41st consecutive quarter of reported profitability with total revenue of $942 million and net earnings of $61.6 million and a second quarter record diluted earnings per share of $ 0.49. During the quarter ,our operating margin expanded to 10 .7 per cent , driven largely by continued lower fuel prices and an increase in ancillary revenue . Total revenue increased by 1.3 per cent year over year, driven by the increase in ancillary revenue which was offset by lower guest revenue resulting from downward pressure on our fares and a lower load factor .
We returned approximately $ 45.1 million to our shareholders through our dividend and share buy - back programs in the second quarter of 201 5 . Since these programs began in 2010, we have returned over six hundred million dollars to our shareholders. At June 30, 2015, our 12 - month record ROIC of 16.0 per cent marks the 12th consecutive quarter of exceeding our goal of a sustainable 12 .0 per cent ROIC and represents an increase of 1 .7 percentage points compared to our 201 4 full - year ROIC of 14.3 per cent . As of the date of this MD&A, we revised our previous ROIC goal from a sustainable 12.0 per cent to a targeted range of 13 .0 to 16.0 per cent.
The overall increase in total revenue was driven by an increase in ancillary revenue included in other revenue , partially offset by lower guest revenue resulting from downward pressure on our fares and a lower load factor . On an ASM basis, for the three months ended June 30, 2015 revenue decreased by 5.7 per cent to 14.16 cents from 15.02 cents in the same quarter of 2014 .
This record ancillary revenue is largely due to WestJets transition to GuestLogix (TSX:GXI) next-generation onboard retail solutions. WestJet continues to leverage the Company’s leading retail platform and PCI-compliant handheld POS devices to transact food and beverage sales on its flights, as well as utilize GuestLogix’ Global Payment Gateway™ for enhanced revenue protection.
Ancillary revenue, which includes service fees, our WestJet RBC ® MasterCard ± program revenue and onboard sales, provides an opportunity to maximize our profits through the sale of higher - margin goods and services while enhancing our overall guest experience by providing guests with additional products and services to meet their needs.
The following table presents ancillary revenue and ancillary revenue on a per guest basis for the three and six months ended June 30 , 2015:
WestJet Vacations continues to generate revenue which supports WestJet’s overall network . The land component, which includes hotels, attractions and car rentals, is reported on the condensed consolidated statement of earnings at the net amount received . In the first half of 2015 , WestJet Vacations’ non-air revenue component declined as the weaker Canadian dollar impacted our margins throughout the first half of 201 5 compared to the same period in the prior year. The majority of the land components are paid in US dollars , which is netted against the gross revenue collected in Canadian dollars.