Reuters and Edmunds's data show used Tesla prices have dropped faster than other car brands.
In July, the average used Model 3, S, X, or Y cost $67,297, but by November, prices fell 17% to $55,754.
Other used car prices only dropped 4% in the same period.
Teslas also stay on used cars lots longer, at 50 days, compared to 38 days for other brands.
Factors like lower gas prices, competition, and high-interest rates contribute to the decrease in Tesla prices.
The decreasing value of used Teslas may affect demand for new cars, according to Karl Brauer of iSeeCars.com.
Previously, people could profit from flipping new Teslas, but that is no longer the case.
Tesla shares have fallen more than 70% this year amid concerns about decreasing demand.