The used prices of fuel-efficient vehicles may soar more than 20 percent in coming months, according to Kelley Blue Book, and dealers should prepare themselves.

With a price spike likely imminent within the next 30 to 60 days, KBB is advising dealers to snatch these fuel-friendly used cars “sooner rather than later.”

Take what happened at the end of February, where in the final week, values of used hybrids, compacts and subcompacts all increased after a slow start to the month.

“The 2010 Toyota Prius led in gains, increasing in value $1,370 through the month of February,” said Alec Gutierrez, senior market analyst of automotive insights for Kelley Blue Book.

Last year, of course, the near-$4/gallon gas led to a similar escalation in the prices of fuel-friendly rides, and the market is in danger of repeating history should fuel prices remain on the same path.

What’s more, the auction value of hybrids on March 2 was 6-percent higher than the price on Feb. 3. Though the subcompact auction value actually dipped 0.5 percent, compacts climbed 0.5 percent between Feb. 3 and March 2.

“Dealers have been aggressively bidding on fuel-efficient vehicles at auction as consumer demand increases in response to rising gas prices,” he continued. “If the past is any indication of things to come, Kelley Blue Book could see values of used fuel-efficient vehicles increase more than 20 percent during the course of the next few months.”

Breaking down the used fuel-efficient vehicle values, prices for hybrids jumped 3.6 percent in the last week of the month. This more than doubled the 1.6-percent increase the week before and was twice as strong as the 1.8-percent uptick the week ending Feb. 17. In the week ending Feb. 10, hybrids dipped 1.1 percent

Meanwhile, fuel-efficient used compact car values climbed 1.3 percent to close February, after gains of 0.1 percent and 0.3 percent the weeks ending Feb. 17 and Feb. 24, respectively. This segment’s prices declined 1.2 percent in the first full week of the month.

Subcompact values were up a more moderate 0.7 percent the last week of the month, but this was up from a 0.2-percent hike the week before, a 0.5-percent downturn the week ending Feb. 17 and a 0.9-percent softening the week of Feb. 10.

Offering a bit of caveat, KBB did emphasize that it will take high fuel costs for the spike in fuel-efficient vehicle prices to persist. In other words, relief in gas prices would likely mean more “normal” values for these segments.