SANTA MONICA, Calif. — Edmunds.com recently discovered that lenders handed out the lowest-ever average annual percentage rates on their auto loans in December.

Site analysts found the average auto loan carried an APR of 4.16 percent, down 0.33 points from November and 0.55 points from December of last year.

Furthermore, Edmunds.com estimated that 15.4 percent of all auto loans carried zero-percent interest — asserting it was the third-highest monthly pace for all of last year.

While so many of December's buyers enjoyed a zero-percent interest rate on their new-vehicle loans, the site discovered many more still managed to avoid exceptionally high APRs.

Analysts learned that only 4 percent of all auto loans carried an APR higher than 10 percent in December. This marked the lowest proportion seen by Edmunds.com since it started gathering data in this category in 2004.

Analysts contend a major contributor to the low December interest rates was the luxury market, which they think is generally driven by an affluent, fiscally stable set of consumers.

The average APR for financed sales of the top seven luxury brands last month was 2.9 percent, the lowest monthly rate of 2010. The site determined the average capped a year in which the average APR in the luxury segment steadily dropped each month since February.

The site pointed out Buick led all makes with the highest rate of financed sales at zero percent APR. Analysts indicated more than half of the brand's financed sales in December were no-interest loans, its highest monthly showing since June 2008.

Toyota placed second for the month with 40 percent of its financed sales at zero percent APR, while Cadillac came in third with one out of every three financed sales enjoying zero percent APR.

Also, Edmunds.com highlighted the attractive financial environment, combined with increased consumer confidence, drove more shoppers to lease new vehicles. December's lease penetration climbed to 23.6 percent, the highest monthly rate since November 2005, the site reported.

"December brought many financially sound consumers back into the market," surmised Ivan Drury, an analyst at Edmunds.com.

"Deal-seekers are generally cautious about their spending and they likely wouldn't enter the market unless their confidence was complemented by the right incentives," Drury added.