NEW YORK (MarketWatch) -- As the rising price of commodities helped bolster the U.S. stock market Tuesday, market watchers keyed on the dollar and what the currency's weakness would mean from here for such commodities as crude oil and gold. Dan Greenhaus, chief economic strategist at Miller Tabak & Co., called gold's spike above $1,000 an ounce and crude's surge above $71 a barrel "symptoms" of the greenback's decline to its lowest level since the fall of 2008. "As the dollar moves lower and expectations continue to look for even further weakness, upward pressure on various commodities including gold and oil will be the order of the day," said Greenhaus. Trading in both crude and gold futures is denominated in U.S. dollars. "Gold is a completely speculative play. It's only worth what someone else is willing to pay for it," said David Kelly, chief market strategist, J.P. Morgan Funds. See more on the action in gold. "Oil is being used more and more as a speculative football, as there is no supply imbalance now (to drive prices up), part of it is people are getting in as an investment," he added. See Futures Movers. On Tuesday, energy and material companies fronted broad market gains as the major indexes extended their advance into a third consecutive session. The Dow Jones Industrial Average (INDU 9,478, +36.35, +0.39%) gained 58.49 points to 9,499.76, while the S&P 500 Index (SPX 1,023, +7.01, +0.69%) added 8.72 points to 1,025.12 and the Nasdaq Composite (COMP 2,031, +11.91, +0.59%) rose 13.91 points to 2,032.67.

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