NEW YORK (CNNMoney.com) -- The decline in residential real estate accelerated though the end of 2007, and home prices in 20 key markets plunged 9.1% for the year, according to a survey released Tuesday.

The S&P Case/Shiller Home Price index showed its largest annual drop in its 20-year history. By comparison, during the 1990-91 recession, home prices fell 2.8%.

Prices dropped faster throughout 2007 with the index recording a 9.1% year-over-year drop in December.

"We reached a somber year-end for the housing market in 2007," said Robert Shiller, Chief Economist at MacroMarkets LLC and co-founder of the index, in a statement. "Home prices across the nation and in most metro areas are significantly lower than where they were a year ago."

All metro areas are now reporting at least four consecutive monthly declines.

Case/Shiller's 10-city index fell even more sharply and finished down 9.8%.

The Case/Shiller indexes compare same-home sale prices. The industry considers them to be among the most accurate snapshots of housing prices.

Of the 20 metro areas examined, all but three posted declines for the year. Miami homes lost 17.5% in value - more than any other metro area - and Las Vegas and Phoenix both had 15.3% declines.

The three that posted modest gains: Charlotte, N.C., 2.3%; Portland, Ore., 1.2%; and Seattle, at 0.5%.

Los Angeles, the nation's second biggest housing market, was the worst performer in December, when prices fell 3.6% compared with November; the decline for the year was 13.7%.

Other double-digit losers for the year were San Francisco, down 10.8%; Tampa, 13.3%; Detroit, 13.6%; and San Diego, 15.0%. Losses in the nation's biggest market, New York, were more modest, down just 5.6% for the year.