Used car prices in April were 0.8% lower than they were in March according to figures compiled by the What Car? used car valuation team.
Compact executives were the best bargain for buyers as their prices dropped by an average of 2.6%.
The only category to see any price rise was MPVs, where prices rose by 0.3%.
Across all categories, the price of petrol cars fell more than diesel. The average price of used petrol cars fell by 1.2% while diesel cars fell by 0.6%.
Retained values in April 2013 have stayed very similar to those in April 2012. One-year-old cars have retained 69.3% of their value, while three-year-old cars have retained 52.4% and five-year-old cars 38%.
4x4s retained the most of their value after one year at 78% while MPVs retained the least at 64.5%.
To find out the value of your car head to the What Car? Used Car Valuations tool.
Great-value used buys based on What Car? figures:
Best buys compact executive
Mercedes-Benz C220 CDI Sport
'10/60, 17,600 miles, 18,990
Bargain 1-year-old nearly new MPV
Vauxhall Zafira 1.7 CDTi Ecoflex 110 Excite
'62/13, 1170 miles, 14,699 (A saving of over 8000 on list price)