US club store operator Costco has booked a jump in earnings for the first nine months of the year as strong sales gains boosted the group’s result.

Net sales for the nine months to 8 May rose 13% to US$59.46bn, including sales from the group’s Mexican joint venture, which Costco began to consolidate into its financial results in fiscal 2011. Excluding this, comparable sales were up 9% in the period, the company said today (25 May).

Costco also revealed that currency exchange and gas price inflation raised the group’s sales totals. Excluding petrol and currency exchange, sales were up 6% during the period.

Net income was $984m, or $2.22 per share, compared to $871m, or $1.95 per share, last year.