Gas prices started a slow but steady decline at the end of May in many areas, but the still-high cost kept car shoppers focused more on fuel-efficient vehicles than their usual trucks and SUVs. According to AutoTrader.com's monthly Trend Engine report, which provides analysis of consumer shopping behavior on the site, many of the trends from April 2011 remained steady in May, from the still-strong interest in smaller cars and the continuing rise in average asking prices across the lists of most-searched new, used and Certified Pre-Owned (CPO) vehicles.