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.

Below are the top 10 Fortune 500 performers (counting down from good to great), based on their closing prices as of Dec. 9.

#10 Centene
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.

#9 Targa Resources Corp.
Ticker: TRGP
YTD stock performance: 48%
Market cap: $1.6 billion
Fortune 500 Rank: 416

Tired of virtually record-low interest rates, income-hungry investors have been on the hunt for dividend stocks, including Targa Resources Corp, which made its public debut in December 2010 and yields a quarterly dividend of more than 3%.

At the start of this month, Targa said it may increase dividend payments by as much as 40% next year, thanks to growth at Targa Resources Partners, which provides natural gas and natural gas liquid services across the country through a limited partnership.

Houston-based Targa also announced major management changes this month that helped boost the stock price. Barclays analysts expect the momentum to continue, targeting the stock at $59 per share, at 53% jump from current levels.

#8 Ross Stores
Ticker: ROST
YTD stock performance: 50%
Market cap: $10.5 billion
Fortune 500 Rank: 303

As high unemployment continues to plague the nation, Americans have been shopping for bargains. That helped Ross Stores, which sells brand-name merchandise at discounts between 20% and 70%, generate strong sales growth every quarter this year.

During both the second and third quarter of the year, when signs of a slowing economy were in the spotlight, overall revenue jumped by a robust 9% during each three-month period, while same-stores sales, a key measure for retailers, grew at a healthy 5%.

Though the discount retailer boasts store locations across 27 states and Guam, it continues to notably grow in big markets. Ross recently opened 12 new stores in Chicago, and has significant plans to expand across the Midwest.

#7 Oneok
Ticker: OKE
YTD stock performance: 55%
Market cap: $8.4 billion
Fortune 500 Rank: 189

As fears of a double-dip recession and Europe's debt crisis gripped markets, investors got defensive and shifted into safe investments, including utilities and dividend-paying stocks. That dynamic favored shares of Tulsa-based Oneok, which distributes natural gas to more than 2 million customers throughout Oklahoma, Texas and Kansas, and pays a dividend of 3%.

Investors are particularly attracted to utility companies when the economic outlook seems dim, since consumers are always in need of gas and electricity.

The company also benefits from its stake in Oneok Partners, which gathers, processes, stores and transports natural gas across the country.

Oneok's stock began to take off in September, after the company raised its 2012 earnings forecast, citing a boost from recently completed projects in the Bakken Shale, Cana-Woodford Shale and Granite Wash oil fields.

#6 Humana
Ticker: HUM
YTD stock performance: 56%
Market cap: $13.8 billion
Fortune 500 Rank: 79

As the second-largest provider of Medicare's managed care plans in the United States, Humana is well positioned to take advantage of the flood of baby boomer retirees.

Roughly 1.9 million Americans are covered by its Medicare Advantage health insurance plans already.

New retirees are already boosting the company's revenues and profitability. Humana reported an 11% jump in third quarter revenue and boosted its 2012 earnings-per-share outlook by roughly 56% after enrollment outpaced the company's earlier forecasts.

Like other companies in the managed care sector, Humana's stock took a hit between 2008 and 2010 as investors feared the effects of health care reform. As the broad outlines of health care reform looked less punitive than expected for managed care companies, investors spent 2011 racing back into the sector.

The company will be undergoing a management shift in the next year. Chief Executive Michael McCallister plans to retire after a decade of serving at the firm's helm.

#5 VF Corp.
Ticker: VFC
YTD stock performance: 62%
Market cap: $14.4 billion
Fortune 500 Rank: 310

VF is the company behind a number of popular brands, including The North Face, Seven for all Mankind, Wrangler, and Vans. In June, VF made a huge move by adding Timberland to its impressive roll.

That acquisition cost VF about $2 billion in cash, but is a "game-changing" one that will spur substantial growth for the next several years, according to Morgan Stanley analysts, who target VF's stock price at $152 per share.

VF said in October that Timberland, which has a strong international presence, added almost $164 million to the company's third-quarter revenue of $2.8 billion. VF CEO Eric Wiseman said he expects that momentum to continue, and boosted the company's fourth-quarter guidance substantially, citing the "transformational" buyout.

Investors are also fans of Greensboro, N.C.-based VF because of its reliable dividend payouts. VF recently marked its 39th consecutive year of higher dividend payments, when it raised its quarterly disbursement 14% to 72 cents per share.

#4 BioGen
Ticker: BIIB
YTD stock performance: 69%
Market cap: $26.6 billion
Fortune 500 Rank: 476

Shares of pharmaceutical maker BioGen spiked on hopes that the company could get its multiple sclerosis pill, BG-12, approved by the Food and Drug Administration.

BioGen develops treatments for multiple sclerosis, cancer and other diseases. Investors are most focused on the prospects for BioGen's MS treatment as analysts have speculated that it could be a billion dollar drug.

In October, BioGen said that patients using BG-12 during a third clinical trial showed significant drops in MS relapse rates.

Analysts estimate that BG-12 could be a $2 billion to $3 billion drug, and become the primary treatment for most MS sufferers. BioGen plans to file for approval with the FDA in early 2012.

BG-12 would round out the company's existing drug portfolio, which helped boost BioGen's third-quarter net income by 38%.

#3 MasterCard
Ticker: MA
YTD stock performance: 69%
Market cap: $43.8 billion
Fortune 500 Rank: 410

The shift to a cashless society has been a boon for credit card companies and helped insulate them from the economic downturn.

For MasterCard, both the number of transactions and their dollar value jumped more than 18% in the third quarter.

MasterCard is the credit card provider best positioned to capture an outsize share of the growing pie of swipes. It has the largest share of customers in emerging markets with roughly half of the company's revenue coming from outside the United States.

MasterCard has also been aggressively investing in technology and expanding partnerships to boost its presence on mobile platforms. Its PayPass technology works with Google's Android Wallet application.

Meanwhile all debit-card companies declared victory on regulations related to debit-card fees. On June 30, the Federal Reserve decided that banks could charge fees of up to 27 cents for a debit-card purchase. That's more than double the original limits proposed under Dodd-Frank regulatory reform.

#2 El Paso
Ticker: EP
YTD stock performance: 81%
Market cap: $19.2 billion
Fortune 500 Rank: 481

The Houston, Texas-based natural gas company announced in October that it had accepted a $21 billion buyout offer from Kinder Morgan, a larger and more diversified energy company.

After moving up steadily for much of 2011, the company's shares shot up after the acquisition was announced and stayed there. (Shares of most of its competitors, which were suddenly deemed takeover targets, did too).

Should it close as expected in early 2012, El Paso's merger with Kinder Morgan would create the largest natural gas pipeline in the US.

Aside from El Paso's lucrative sales price, it's been a good year for natural gas producers overall, thanks to an uptick in demand for domestic gas.

It's not all smooth sailing. Environmentalists continue to push against "fracking," a process that injects water, sand and chemicals deep into the ground to break up the shale and release natural gas. Opponents say the process is contaminating drinking water and polluting the air.

#1 WellCare Health Plans
Ticker: WCG
YTD stock performance: 93%
Market cap: $2.2 billion
Fortune 500 Rank: 420

As the first wave of baby boomers turns 65, WellCare is well poised to boost to take advantage. The Tampa, Fla., managed-care provider is the fourth-largest provider of Medicare Advantage insurance plans to seniors in the United States.

Medicare Advantage, also known as Medicare Part C, is another option for Medicare recipients that mirror traditional insurance plans or offer supplemental coverage.

In April, WellCare settled a 2008 fraud scandal involving falsifying health records. The settlement cleared the way for WellCare to once again be a government contractor for the Medicare and Medicaid programs.

WellCare's enrollments jumped 10% in the third quarter, mostly due to an increase in Medicare Advantage members. The increase helped the firm nearly double its third-quarter profits and raise its outlook.

WellCare also become a possible takeover target. Major health insurers have been scrambling to increase their market share in privately-managed Medicare plans, with UnitedHealth Care and Cigna (CI) already acquiring large Medicare Advantage providers this year.