IRVINE, Calif. -

Kelley Blue Book offered a word to the wise on Tuesday for dealers looking around for fuel-friendly rides: “shop with caution.”

And wait.

The wave of rising used values for compact, subcompact and hybrid cars has finally crested and some softening is beginning to show up, according to Kbb.com, which suggested the declines will likely remain through the beginning of summer.

“Regardless of where these used-vehicle values end up, fuel-efficient vehicles will remain a smart purchase for budget-conscious consumers,” stated Alec Gutierrez, manager of vehicle valuation for KBB.

“Our advice to dealers and consumers is to shop with caution today, since values are likely to fall through the early part of summer,” he continued. “If possible, it would be best to hold off on purchasing a fuel-efficient vehicle until after summer, when values should be more stable.”

Fuel-friendly vehicles had seen their values move up for 20 straight weeks, climbing almost 25 percent during this time frame. In light of dissipating fuel prices, subcompact, compact and hybrid car values are moving downward, something that hasn’t happened in five months.

“In fact, Kelley Blue Book analysts currently see values for some of these vehicles dip into the red for the first time since January,” KBB highlighted.

Breaking some of KBB’s analysis down, the value of compact cars on Friday was down 0.3 percent compared to May 27.

Likewise, hybrids were off 0.3 percent and subcompacts were down 0.1 percent. Overall, the industry was down 0.4 percent.

Through Friday, the year-to-date change for these segments is still well above the industry average, which is an increase in value of 5.4 percent. Compact cars are up 21.4 percent year-to-date, with hybrid cars up 20.4 percent and subcompact cars up 22 percent.

Gas prices, of course, have been the primary impetus for this value increase in 2011, KBB indicated. However, the national average hit an apex in May when it reached $3.98/gallon.

It has subsequently dropped consistently to the latest level of $3.71/gallon, according to KBB.

Interestingly enough, OPEC said on Wednesday of last week that there would be no change in crude oil production. Then on Friday, OPEC member Saudi Arabia said it would boost crude oil production by 13 percent from May and pumped out a daily sum of 10 million barrels.

Officials believe this points to fuel prices remaining on a downward slope the rest of summer. As such, fuel-friendly rides will see their demand — and thus, prices — dip.

Should Saudi Arabia actually go through with the production hike, KBB projects another 3-percent to 5-percent slide in used-vehicle prices.

Furthermore, a national fuel price average of under $3.50/gallon will accelerate that drop, KBB added.