Wal-Mart de Mexico (Walmex) is set to announce a sales increase of five per cent for July, a weaker return than in June due to fierce advertising competition with rival retailer Soriana and the calendar effect of having one less Sunday in the month.

June same-store sales jumped 8 per cent this year, according to Reuters, while in July 2007 sales at stores open for 12 months or more rose by 2.1 per cent.

Walmex recently launched a marketing campaign to run against Soriana, which has been pushing its brand in new markets such as Mexico City with three-for-two deals and a loyalty card scheme.

Sales have been hit by soaring food and fuel prices that have led to consumers reigning in their spending.