Although the S&P 500 Index was trading in the positive for most of Monday's afternoon session, it took a dive in the last hour of trading as its energy components sold off heavily.

The S&P 500 Index dropped 1.16 points, or 0.10 percent, to close at 1,108.01.  The Dow Jones Industrial Average dropped 19.04 points, or 0.18 percent, to close at 10,383.31. 

The dollar, which slid down against the euro for most of the U.S. session, rallied about 10 pips in the last 30 minutes of the afternoon U.S. stock session.

Energy companies were among the steepest decliners, particularly those involved in natural gas.   Southwestern Energy (NYSE:SWN) closed down 3.53 percent and Williams Companies (NYSE:WMB) closed down 2.97 percent.

Denbury (NYSE:DNR), which is involved in oil and natural gas, dropped 3.05 percent and Schlumberger (NYSE:SLB), which announced its merger with Smith International (NYSE:SII), closed down 3.65 percent.

Although most energy prices rose on Monday, natural gas tanked as its NYMEX March future dropped 2.36 percent.

U.S. banks rallied as JPMorgan (NYSE:JPM) closed up 2.05 percent and Wells Fargo (NYSE:WFC) gained 1.83 percent.

The financial sector traded higher earlier in the afternoon session but participated in the late selloff.

Health insurance firms generally held on to gains in the last half hour of trading in spite of uncertainty surrounding President Obama's healthcare proposals unveiled this morning.

Humana (NYSE:HUM) closed up 5.56 percent and UnitedHealth Group (NYSE:UNH) closed up 2.79 percent.

House Republican Representative David Camp said the proposal was not a serious attempt to address the concerns the American people have expressed about the Democrats' bills.

Of Obama's upcoming bipartisan televised healthcare summit on Thursday, Camp warned that if the starting point for this summit is more of the same backroom deals and partisan bills, then this meeting will likely be a charade.

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