NEW YORK (CNN/Money) - There may still be time for investors to get a good buy on oil stocks, but only if they're in it for the long term, analysts say.

Shares of major oil producers failed to participate in the past week's oil-price rally to $25 a barrel, in part because they already had enjoyed a six-week rally from their 2001 lows, analysts say.

But the expectations are that oil stocks could be poised for a rise later this year and in the long term. So while investors might have been better off buying oil stocks six weeks ago, there still may be time for those who are willing to buy and hold. The companies that could be affect include the major oil exploration and production companies such as ExxonMobil (XOM: Research, Estimates), ChevronTexaco (CVX: Research, Estimates), or Phillips Petroleum (P: Research, Estimates) and Conoco (COC: Research, Estimates), which are awaiting final approval of their proposed merger, and the oil-service companies such as Schlumberger (SLB: Research, Estimates) and Halliburton (HAL: Research, Estimates).

The prices of oil and oil-related stocks suffered in late 2001 as worries grew about a global recession and flagging demand in the aftermath of the Sept. 11 terrorist attacks. For example, the price of Brent crude fell as low as $19.40 in the last quarter of 2001, and shares of industry behemoth ExxonMobil hit a December low of $36.44.

But oil finally has rallied in the past week, with the average price of a barrel of oil reaching and holding at $25. Natural gas prices also have come up a lot recently -- at $3.50 mcf (thousand cubic feet), at the high end of forecasts for this year, said Gene Gillespie, senior energy analyst at energy boutique Howard Weil in New Orleans.

Since oil-related stocks already had rallied nicely in the past six weeks, with ExxonMobil, for example, rising from $38.40 at the close on Feb. 12 to $43.68 Tuesday, they haven't gained any ground on crude's rise. Gillespie notes that shares of the major oil companies have appreciated by about 9 percent in the past 52 weeks, excluding dividends, while the S&P 500 index remained fairly flat.

Analysts think the lack of a run-up in the stocks during the past week is warranted because they think the price of oil has risen too far, too fast. Any investor who buys now expecting a short-term gain could be disappointed if, as many expect, the price of oil backs off in the coming weeks.

"I think that the present valuations don't fully reflect the higher prices, but I think there's a potential for the commodity price to come down" in the near term, said John M. Selser, an analyst at the New Orleans energy research and sales firm Johnson Rice.

Tyler Dann, analyst at Banc of America Securities, thinks the integrated oils at present are 9 percent above fair value, according to a March 25 research report. The $25-a-barrel price, Dann argues, "is well above what we view as a long-term sustainable oil price of $20 a barrel." The price of crude has been driven up, in part, on belief in the strength of OPEC's five million barrel-per-day production cuts, but mainly on speculation that the supply of oil would be interrupted if the United States takes military action in Iraq, he said.

But there is broad agreement among analysts that any supply interruption resulting from military action would be short-lived. Selser notes that Iraq's two million barrels-per-day could easily be replaced by a partial rescission of OPEC's five-million-barrel production cut.

Assuming that the price of crude does drop back soon, Sesler thinks oil stocks also could come back down for a while. "But after that happens, there's a potential for them to trade even higher than they are now," he said.

With an improving economy expected to drive petroleum-product and crude-oil volume higher, Gillespie and others think the long-term outlook is good.

"I think the majors are very fairly priced here. They're not unattractive. In fact, they're somewhat attractive longer-term," Gillespie said.

Philip L. Dodge, oil analyst at Ryan Beck & Co., thinks oil prices appear poised for relative stability, which is good for the stocks. "I think they'll be quite a bit higher later this year," he said.

Oil-service stocks such as Schlumberger also could be a good call for long-term investors, Dodge noted. "There's always a lag between when the oil prices go up and when the oil companies start spending more money on drilling and services," Dodge said. So while he thinks the oil majors will post improved earnings for the quarter ending in March, he doesn't expect oil-service stocks to show earnings improvement until the September quarter.

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But Dodge reminds investors that the market often trades ahead of reported earnings improvement. So while he thinks there's still time for investors to get shares of either oil-service companies or the majors, the clock is ticking.