McColl's said like-for-like sales for the 13 weeks to 28 August were down by 1.8 per cent and total revenue was up 1.8 per cent for the quarter.
Sales in McColl's newsagents performed particularly badly, down by 3.7 per cent. Premium convenience store sales - including sales in wine stores - decreased by 1.2 per cent.
In recently bought stores, sales increased by one per cent.
Why it's interesting
McColl's attracted attention recently when it secured a £117m deal with the Co-op to take on 298 of its stores.
Read more: The Co-op's having a retro rebrand
The agreement - part of the Co-op's turnaround strategy - is set to be approved by shareholders at a meeting on 19 September. Taking on the stores will help McColl's reach its target of delivering 1,000 convenience stores by the end of 2016.
What McColl's said
Jonathan Miller, chief executive of McColl's, said: "2016 continues to be a year of significant progress in delivering our convenience strategy. This was particularly demonstrated by our transformational acquisition of 298 convenience stores from the Co-op announced on 13 July. We are making good progress with the approvals and our preparations ahead of the transition of these stores during 2017."
He said the company was "on track" to meet the board’s expectations for the financial year.