Fortune 500: Top-performing stocks of 2011

It's been a hot and cold year for the stock market, but these Fortune 500 companies managed to float to the top with impressive gains. From Ross Stores to MasterCard, here are the biggest winners.

From 30,000 feet, this year's volatile swings in the stock market don't look as bad, with the S&P 500 down only 3% for the year.
Fortune 500 companies took the middle ground, with half of those companies posting gains. Roughly 30% enjoyed double-digit percentage stock increases.
Among the best performers were companies like MasterCard, which benefited because a change to debit fee regulation was not as bad as first feared. Retailers also fared well as consumers began to loosen those proverbial purse strings.

Ticker: CNC

YTD stock performance: 48%

Market cap: $1.8 billion

Fortune 500 Rank: 493

Shares of Centene, which provides managed care programs and related services to individuals under Medicaid, surged as the company continued to add more members and expand into new states, including Florida, Illinois, Mississippi and Texas.

In its last quarterly report, St. Louis-based Centene boasted 1.6 million members, up almost 8% from a year ago. Investors were also pleased that the company raised its outlook for the year.

Centene's stock has also benefited from talk that the managed-care provider could be ripe for a takeover, following a slew of acquisitions by major health insurers of smaller companies that specialize in covering Medicaid patients.

Wells Fargo analysts say the company is also likely to benefit from health reform, since it is set to substantially expand Medicaid eligibility. Cash-strapped states have already started looking into shifting recipients to managed-care providers, which have promised to keep costs low.