Nine out of ten people have been forced to abandon an online transaction because the application failed before completion.
As a result more than half of those dumped midway through their transaction either had to waste more time contacting the company concerned - or have given up and gone to a rival firm.
According to network traffic management outfit, CatchFIRE Systems, two thirds of those transactions - such as booking flights or buying consumer goods - were valued at more than £200.
The most serious complaint among those quizzed detailed Web sites that crashed at the end of a transaction or while the payment was processing - forcing consumers into repeating the operation, or making time-consuming calls to check if the purchase was successfully completed.
One of those surveyed Bethan Gray, 28, a furniture designer from London, said: "The site crashed when I was buying flights on-line and I lost the whole form which I spent ages filling in. Then I was really worried that I had bought the flights twice so wasted 15 minutes calling the company up to check even though I hadn't."
Barrister, David Griffiths, 29, said: "I was booking a holiday when the site crashed six times after my credit details having being inputted - so I just gave up."
In a statement CatchFIRE Systems (Europe) marketing director, Nigel Thomas, said: "Poor web site performance is still plaguing the on-line industry.
"Consumers being kicked off Web sites during purchases is like someone being thrown out of a restaurant in the middle of a meal - it is inexcusable.
"Our research shows that on-line consumers have zero tolerance for delays. They don't think twice about abandoning transactions if they are kept waiting," he said. ®