Direct Excellence is calling on the motor insurance industry to change its quoting process, enabling consumers to compare premiums.
The price comparison agency said that it is still very difficult for consumers to compare motor premiums because of the wide range of excesses used.
Research by the company found that average excesses varied by over 36% from £192 to £263. Meanwhile, for the same risks the spread of premiums ranged from an average of £380.90 to £486.02, a variance of 28%.
Direct Excellence said: "There is no obvious correlation between excess and price. So customers trying to get a clear price comparison are going to have a difficult time."
The company called for the industry to make comparisons easier by letting consumers choose the excess, allowing for easier "like-for-like" comparisons.
It said: "A small number of companies are now changing their quoting processes and asking the customer to choose a preferred excess level rather than simply telling them at the end of the call which excess the agent has chosen for them.
"This is a huge behavioural change in the industry - and worth recommending to those that have not yet adopted the practice."