YAHOO [BRIEFING.COM]: Efforts to prevent contagion in Europe helped the stock market stage its best single-session rally in more than one year. And even though the move was both broad and strong and accompanied by high volume trade, some question its sustainability.

A positive mood permeated global trade for the entire session, thanks to a decision by leaders of the European Union (EU) and International Monetary Fund (IMF) to pledge financial support to eurozone countries. In turn, Greece and other countries on tenuous financial footing will be able to tap a pool of 500 billion euros from the EU, while the IMF stands ready with another 250 billion euros. In addition to those measures, the European Central Bank announced that it will make eurozone bond purchases via the secondary market. Such a move should help facilitate credit markets by providing a deep pocketed buyer. Meanwhile, the U.S. Federal Reserve has reopened swap lines with foreign institutions.

That series of efforts helped tighten credit default swap spreads for the likes of Greece and Portugal, and also sent the euro up sharply. The euro gave ground against bounce by the greenback, though; in turn, the dollar settled trade with a loss of little more than 0.2% after it had been down as much as 1.8% against a basket of competing currencies.

Stocks traded with strong gains for the entire session, especially those in Europe, where all 30 names in Germany's DAX advanced and all 40 components of France's CAC climbed. French banks booked some of the best gains as the bailout news helped relieve concerns related to their loan exposure to Greece.

Many market pundits questioned whether this session's surge was anything more than a relief rally for the broader market, especially after the S&P 500 fell almost 8% during the course of the four previous sessions.

Bets on further moves to the downside caused some to cover their positions this session. That sort of short covering only squeezed stocks higher and ushered in higher trading volume.

With some 1.8 billion shares exchanging hands on the NYSE this session, trading volume surpassed its 200-day moving average for the fifth time in a row.

Commodities bounced off nearly a 3-month low to close 1.6% higher this session. Gains in the index dissipated throughout the morning as the dollar index rose all session, though.

The largest gains were seen in energy commodities, they closed up 2.9%. June crude oil bounced off a near 3-month low to close up 2.3% at $76.80 per barrel. July natural gas saw an even more pronounced gain, closing 3.7% higher at $4.17 per MMBtu.

Gold was one of the few commodities that did not benefit from short-covering this session. June gold closed 0.8% lower at $1200.80 per ounce. Meanwhile July silver closed 0.5% higher at $18.55 per ounce.

Though some may discount the conviction behind this session's move and attribute it to relief buying and short covering, nearly 98% of the names in the S&P 500 advanced to take the stock market to its best percentage gain in more than 52-weeks. Such broad-based strength sent the Volatility Index, or "fear gauge," to a 30% drop.

Advancing Sectors: Industrials (+5.7%), Financials (+5.6%), Consumer Discretionary (+5.3%), Tech (+5.0%), Materials (+4.8%), Energy (+4.0%), Utilities (+3.0%), Consumer Staples (+2.8%), Health Care (+2.7%), Telecom (+2.4%)
Declining Sectors: (None) DJ30 +404.71 NASDAQ +109.03 NQ100 +5.0% R2K +5.6% SP400 +5.2% SP500 +48.85 NASDAQ Adv/Vol/Dec 2209/2.78 bln/327 NYSE Adv/Vol/Dec 2988/1.86 bln/157