Residual values of full-size vans have remained strong while compact vans have weakened in the past year, creating a widening gap that has created two used van markets for fleet sellers.

The residual values of three- to five-year-old compact vans have deteriorated since late 2014 — a trend that's expected to continue as long as fuel prices remain low and buyers can opt for new Euro-style models, according to Black Book.

"Compared to the car segments, they're still doing well," said Anil Goyal, Black Book's vice president of automotive valuation and analytics. "But they kind of lost ground last year when the gas prices fell, and have continued to slide since then."

Compact vans have ranked toward the top of depreciation reports for several months. In January, the category fell 3.6% to $10,101 and 22.8% from a year earlier. The category showed the highest depreciation of any vehicle category tracked by Black Book for 2015, falling 22.6% to $10,478. Meanwhile, full-size vans depreciated only 5.7% to $20,068 in 2015. These figures represent an average of sales for vehicles in model years 2010 to 2014.

Part of the slump has resulted from an oversupply of first-generation Ford Transit Connect vans gobbled up by commercial buyers after a 2009-MY update. At the time, with fuel prices high and the economy slumping, many commercial fleets downsized to the Transit Connect from full-size vans for reduce operating costs.

But these vans now entering the used-vehicle market, especially from model years 2011-MY to 2013-MY, have created more supply that demand. Ford gave the Transit Connect a wide-ranging makeover for the 2014-MY.

"At that time, pricing was right, the economy was struggling, and gas prices were high," Goyal said. "It really became a hit. The production was accelerated too quickly, so a lot of supply got generated."

With a 2011-MY used full-size van now costing only about $2,500 to $3,000 more at auction, buyers are opting for the larger vehicle.

Full-size vans have also held their value much better than their smaller brethren. Comparing two 2011-MY vehicles, a full size van will typically be selling at about 47% of its initial value, while a compact van will sell for about 40% of its initial value, Goyal said.

Older compact vans have also been hurt by a glut of new product in the segment. General Motors introduced its 2015-MY Chevrolet City Express at the end of 2014, and FCA US began selling its 2015-MY Ram ProMaster City at the beginning of the year. Mercedes-Benz introduced its Metris mid-size van in the fall, a vehicle Black Book will categorize as a compact van when it's sold at auction.

These introductions resulted in an increase in new compact van sales of 37.6% to 94,167 units in 2015, according to GoodCarBadCar.net. In 2013, manufacturers sold about 53,000 compact vans. New Transit Connect sales increased 20.9%, according to Ford.

Despite these factors, Goyal doesn't see compact van depreciation getting much worse.

"The depreciation has been much steeper," Goyal said. "But if you look at the pricing, there is still a little more room for it to run before that disparity becomes so large. The prices are not going to drop much more but should remain low."