A round of healthy quarterly earnings, a spate of mergers and the promise of another strong season have been pushing oil refiners steadily upward for months, and several analysts say stock prices now reflect the sector's strong fundamentals.

The stocks of many of these companies, such as

Sunoco

(SUN) - Get Report

,

Texaco

(TX) - Get Report

and

Valero Energy

(VLO) - Get Report

are hovering near their 52-week highs. And they've been gaining at a rapid pace.

"Their earnings are going to be strong, but we think the run-up in the stock price reflects that," said Corey McElveen, a stock analyst with

Morningstar

. "The stocks are fully valued."

Valero was up 21 cents to $51.80 on Monday. Its stock has jumped almost 44% in the last six months and recently hit a 52-week high of $52.60.

Ultramar Diamond Shamrock

( UDS), which is being acquired by Valero, is up 100% in the same period.

McElveen attributes the recent run-up in prices to a combination of strong earnings reports and investors' anticipation of a strong summer -- when many motorists hit the roads and drive up demand for gas. Indeed, with refiners running near capacity and gasoline prices near record highs, profits are expected to be spilling over for refiners during the summer. Crude oil prices have been rising steadily since mid-March and are currently at their highest level since mid-February. June crude oil futures on the

New York Mercantile Exchange

were recently trading at $29.95 a barrel.

Fueled by higher prices and strong demand, many oil companies have recently surpassed analysts' earnings expectations. McElveen said he expects refiners to produce strong results in the next quarter and beyond. Still, he says, now is not a good time to buy.

Prudential's

Andrew F. Rosenfeld, a refinery equities analyst, agrees that stock prices are reflecting oil stocks' positives. "Last Friday, we downgraded the sector from a buy to a hold. This isn't the time to be putting your money into them because we think we're in the upwards part of the cyclical refining cycle," he said. Rosenfeld expects the current energy cycle to last three years, with another 12 to 18 months left in it. "It's more to the point now where we've seen most of the stock appreciation."

Prudential downgraded

Tosco

( TOS), Ultramar, and Valero to hold. "In our view strong refining industry fundamentals have been the catalyst moving the stocks towards our upside potential prices: the group is now on average 9% below these prices. While we believe there remains additional upside in the stocks due to the continuing strong refining fundamentals, we are of the opinion that most if the group's likely outperformance has been achieved," he wrote in the research report.

Sunoco

(SUN) - Get Report

, which has a 52-week high of $42.61, gained 42% in the last six months, while

Texaco

(TX) - Get Report

is up 18% in the same period.

Royal Dutch Petroleum

( RD), the parent of

Shell

, is essentially unchanged in the last six months. Shell tried to buy

Barrett Resources

( BRR), which is instead being bought by

Williams

(WMB) - Get Report

.

TheStreet.com

recently took a look at refiners and the

the current spate of mergers.