The Grocer 33 six-month review, published this week, shows some major stores are racking up nearly twice the number of out of stocks compared with the first half of the year.
Somerfield's performance was by far the weakest, with 48 out of stocks in the past 26 shops conducted - 22 more than previously.
Sainsbury's, which has implemented a number of initiatives to boost availability during the year, clocked up 30 - almost double the number recorded in the previous six months. Meanwhile Waitrose, which was voted the best retailer for availability in The Grocer 33's End of Year Review on June 10, had 25 out of stocks, 16 more than previously. It plunged to fourth place in the availability charts.
Tesco was out of stock in 23 items during the period compared with 16 previously. Asda chalked up 19 out of stocks in the past six months, just two more than in the first half of the year. Morrisons put in the best performance in terms of availability. But even that chain's score of 97.85% was below that achieved six months ago.
One expert said a preoccupation with other matters may have distracted the major multiples.
"The supermarkets definitely appear to have taken their eye off the ball with regards to availability," said Tim Kershaw, chief executive of supply chain consultancy Libra Europe. "They have had a multitude of other issues to contend with, such as reducing waste, and it would seem availability has slipped down the agenda.
"This is bad news for the industry, as availability is an incredibly big issue with consumers."
The Grocer 33's six-month review also reveals that Asda has continued to dominate the pricing tables in the second half of this year.
It has claimed The Grocer 33's cheapest shopping basket for 18 of the past 26 weeks, compared with Tesco's five, Morrisons' two and Sainsbury's one.