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BOSTON ( TheStreet) -- TheStreet.com's stock-rating model upgraded oil-and-gas transporter Enbridge ( ENB - Get Report) to "buy."

The numbers: Second-quarter net income fell 40% to $395 million, or $1.08 a share, as revenue decreased 26% to $2.9 billion. Its gross margin rose from 9% to 16% and its operating margin climbed from 5% to 10%. The company has a precarious financial position, with $354 million of cash, compared to $12 billion of debt. A debt-to-equity ratio of 1.7 demonstrates higher-than-ideal leverage.

The stock: Enbridge has advanced 26% this year, more than the Dow Jones Industrial Average and S&P 500 Index. The stock trades at a price-to-earnings ratio of 11, a discount to the market and oil and gas transportation peers. Shares pay a 3.4% dividend yield.

The model upgraded machinery maker Ingersoll-Rand ( IR - Get Report) to "hold."

The numbers: Second-quarter net income fell 52% to $122 million and earnings per share dropped 54% to 41 cents. Revenue grew 13% to $3.5 billion. Its gross margin fell from 32% to 30% and its operating margin declined from 13% to 8%. A quick ratio of 0.7 reflects less-than-ideal liquidity. A debt-to-equity ratio of 0.7 indicates reasonable leverage.

The stock: Ingersoll-Rand has risen 85% this year, outpacing major U.S. indices. The company posted losses in the previous two quarters. The stock pays a 0.9% dividend yield.

The model upgraded mass-marketing specialist Valassis Communications ( VCI) to "hold."

The numbers: Second-quarter net income surged 141% to $16 million and earnings per share jumped 135% to 33 cents. Revenue declined 9% to $544 million. Its gross margin rose from 25% to 27% and its operating margin increased from 6% to 8%. The company has adequate liquidity, evident in its quick ratio of 1.3. A debt-to-equity ratio of 25 reflects excessive leverage.

The stock: Valassis has multiplied more than 10-fold this year, trouncing major U.S. indices. The company posted a loss of $4.63 a share in its fourth quarter. The stock doesn't pay dividends.

The model upgraded battery maker Exide Technologies ( XIDE) to "hold."

The numbers: The company's fiscal first-quarter loss widened to $54 million, or 71 cents a share, from a loss of $10 million, or 14 cents a share, in the year-earlier period. Revenue fell 39% to $593 million. Its gross margin rose from 20% to 22%, but its operating margin fell into negative territory. A quick ratio of 1 reflects adequate liquidity. A debt-to-equity ratio of 2.3 demonstrates excessive leverage.

The stock: Exide Technologies is up 44% this year, beating major U.S. indices. The company has suffered from erratic operating results over the past year. The stock doesn't pay dividends.

The model upgraded Zimmer Holdings ( ZMH), a maker of reconstructive implants, to "buy."

The numbers: Second-quarter net income fell 7% to $210 million and earnings per share dropped 1% to 98 cents, cushioned by a lower share count. Revenue declined 6% to $1 billion. Its gross margin rose from 82% to 85%, but its operating margin remained steady at 30%. A quick ratio of 1.6 reflects ample liquidity. A debt-to-equity ratio of 0.1 indicates modest leverage.

The stock: Zimmer Holdings is up 29% this year, more than the Dow and S&P 500. The stock trades at a price-to-earnings ratio of 15, a discount to the market and health care equipment peers. The company doesn't pay dividends.

-- Reported by Jake Lynch in Boston.