New listings were down last month by almost 6% on August the year before, and down 13.1% on a monthly basis.
Analysis of new listings on website Home has shown that in 100 UK towns and cities, supply dropped on a monthly basis in two thirds of places.
The biggest falls were in Coventry (down 33%), Winchester (31%), Salford (28.5%) and Oxford (25.6%).
In London, supply was down 22.3%, with the highest monthly fall in Richmond at 42%.
The analysis was done by HouseSimple, whose CEO Alex Gosling said: “Few people will be concerned by the drop-off in new listings between July and August.
“More of a concern is the 5.9% drop-off when comparing last month with the corresponding month in 2016. Supply continues to be a major issue.
“The property market needs a strong September after a subdued period since the general election.”
The Land Registry has said that transactions in the second quarter of this year fell 12% on an annual basis across England and Wales. In the 12 months to the end of the quarter, there were 844,380 transactions – the lowest since the same period in 2009/10.