Its share of the market rose to 16.6 per cent for the 12 weeks to July 16, compared to 16.5 per cent last year.
Shopper spending at Asda grew by 6 per cent, ahead of total grocery growth of 4.2 per cent. The grocer and general merchandise giant currently has the second-largest food market share of the grocery market.
Tesco continues to hold the number-one position, and this month boosted its share by 0.1 per cent to reach 31.5 per cent.
In third place, Sainsbury's maintained its market share of 16 per cent for the fifth consecutive month, up from 15.8 per cent for the same period in 2005. Morrisons also held onto its 11.3 per cent share.
Both Somerfield and Waitrose continued to grow their market share, to 4.2 per cent and 3.8 per cent respectively.