Disappointing earnings reports, sliding energy shares, bad inflation news and volatility ahead of Friday's options expiration sent major indices tumbling Thursday, unwinding all of Wednesday's rally and more.

But if the market's flip-flop pattern is to resume Friday, postclose earnings from (most notably) Google ( GOOG) and SanDisk ( SNDK) may be the catalysts for a rebound Friday. The search-engine giant handily beat Wall Street expectations, and its shares were recently up 9.5% in after-hours trading. SanDisk shares were recently up more than 15% after its own upside surprise.

The after-hours action was in sharp contrast to Thursday's regular trading day when the Dow Jones Industrial Average slumped 133.03 points, or 1.28%, to 10,281.10. The blue-chip index was weighed down by a disappointing earnings report from Pfizer ( PFE), which fell 9%, and McDonald's ( MCD), which fell 4%.

A slide in crude oil prices and energy shares also took down Dow component Exxon Mobil ( XOM), which fell 3.5%.

Sliding oil prices slammed energy stocks but eased inflation concerns in the bond market, where the benchmark 10-year Treasury bond finished up 7/32, its yield falling to 4.43%.

The trading session had begun on a downbeat note after disappointing results Wednesday evening from eBay ( EBAY), which fell 6.8%. And there was more bad news before the open after Pfizer, McDonald's and Ford ( F) reported.

The S&P 500 finished down 17.96 points, or 1.50%, at 1177.80. The Nasdaq Composite lost 23.13 points, or 1.11%, to finish at 2068.11.

The downdraft became more pronounced as crude oil prices slid throughout the session, taking with them the energy sector. Crude oil finished at $61.03 per barrel on Nymex, down $1.38 on the day, after briefly trading below $60.

While crude oil finished off lows, the energy sector fell further after the 3 p.m. EDT close of Nymex trading, before getting a modest bounce just before the stock market's 4 p.m. close. The Amex Oil Index slid 4.5% to 912.63 vs. an earlier low of 903 but well off its intraday high of 957.

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