BOSTON ( TheStreet) -- The following companies have annual revenue of more than $500 million, below-average valuations, debt that is less than 49% of total capital, and receive "buy" ratings from our proprietary quantitative model, which considers more than 60 factors. They are ordered by their potential to appreciate.New Jersey Resources ( NJR) is an energy-services company that provides retail and wholesale energy services to customers in New Jersey and other states from the Gulf Coast to New England and Canada. The numbers: Fiscal second-quarter revenue declined 20% to $938 million as earnings surged 183% to $36 million, or 83 cents per share. The debt-to-equity ratio is low at 0.6. But a quick ratio of 0.4 indicates a weak cash position. Margins improved significantly during the quarter, with operating margin climbing past 6% and net margin jumping to 4%. The stock: New Jersey Resources is flat in 2009, underperforming the Dow Jones Industrial Average and S&P 500. The stock trades at a fair price-to-earnings ratio of 14 and offers an attractive 3.2% dividend yield. Advanced Auto Parts ( AAP) sells aftermarket automotive parts, accessories and maintenance items. The numbers: First-quarter revenue increased 10% to $1.7 billion as earnings rose 14% to $94 million, or 98 cents. The operating margin remained stable at 9% and the net margin improved from 5% to 6%. Just $51 million of cash reserves and a quick ratio of 0.1 indicate a weak liquidity position. But a debt-to-equity ratio of 0.3 demonstrates modest leverage. The stock: Advanced Auto Parts has climbed 37% in 2009, beating major U.S. indices. The stock trades at an expensive price-to-earnings ratio of 18 and offers a dividend yield below 1%.