Prices in key housing markets nationwide continued to tumble during August, a key report said on Tuesday morning. The Standard & Poor's/Case-Shiller home price indices posted their umpteenth record annual decline in August, with a 10-city index falling 17.7 percent and a 20-city index falling 16.6 percent, S&P said in a press statement. Prices fell roughly 1 percent across all 20 cities between July and August, according to the index data. "The downturn in residential real estate prices continued, with very few bright spots in the data," says David Blitzer, chairman of the index committee at Standard & Poor’s. "For the fifth straight month, every region reported negative annual returns. This started when Charlotte, NC, was the last region to turn negative back in April 2008." Read the full Case-Shiller report. Both the 10-City and 20-City composites indices have been in year-over-year decline for 20 consecutive months, Blitzer noted. Of the 20 regions tracked in the S&P data, 13 saw annual returns worsen during August relative to July -- suggesting that the decelerating trend being highlighted in other housing data is at least contradicted by trending in the Case-Shiller data. (Relative to some other datasets, the S&P/Case-Shiller data is more geographically limited). Prices drop as foreclosure sales heat up Nine of the 20 regions tracked posted record annual declines in August, S&P said. Phoenix and Las Vegas are now returning -30.7 percent and -30.6 percent versus Aug. 2007, respectively. And while the Case-Shiller data doesn't track sales volume, it seems clear that rising transaction volume on foreclosed real estate is helping push down home prices even further -- especially in some of the nation's hardest-hit markets. For example: Miami and Tampa, the two key Florida markets, were down 28.1 percent and 18.1 percent, respectively, during August. Not everyone is convinced, however, that the uptick in foreclosed real estate sales portends a possible view to the bottom in the nation's housing markets. Analysts at Banc of America Securities reiterated an earlier warning late last week that such an increase in home sales may actually serve to exacerbate pricing problems by placing further borrowers underwater and under duress. Only two regions tracked by the Case-Shiller data posted positive monthly returns in August: Cleveland, which saw prices rise 1.1 percent, and Boston, which returned a barely-there 0.1 percent. Boston has eked out positive returns for five months now, while Dallas and Denver saw their previous streak of four months of positive returns come to an end. Dallas -- regularly cited as one of the nation's stronger housing markets, the city has now seen prices fall 2.7 percent year-over-year, S&P reported. For more information, visit Write to Paul Jackson at