By Karen Nickel

(FORTUNE Magazine) – Last year was a dry hole for the owners of oil service stocks. Faced with low oil prices and a slump in drilling, the big oil service shares fell 20% on average. But one stock bucked the trend. Schlumberger, a $6-billion-a-year oil service company headquartered in New York City and Paris, posted higher operating earnings, up 16%, and enjoyed a respectable 8% increase in share price. Analysts say that's just the beginning. As the industry outlook improves, Schlumberger stock should become a gusher. Believers include Bill Mankivsky, manager of the Fidelity Select Energy Services Portfolio, who has made Schlumberger his largest holding. Says he: ''If one stock is going to have a good year in 1992, it has got to be Schlumberger.'' The recovery in drilling is expected to be slow in the U.S. But Schlumberger draws an estimated 90% of its profits from abroad, where drilling activity is improving more quickly. It is also strong in the fastest-growing international markets, Africa and South America. Says Charles Ober, an oil industry expert at T. Rowe Price's New Era natural resources stock fund: ''Schlumberger has an international infrastructure that's second to none.'' It's a technological leader too, thanks to the largest research budget in the industry -- $400 million last year. In today's sluggish environment, analysts say that oil service companies with the best technology will grab an increasing share of the business. One of Schlumberger's most promising new ! products is the Maxis 500, a lab in a truck that does on-the-spot geological analysis of a drilled hole. For tricky horizontal and offshore drilling, the company offers instruments that, attached to the drill assembly, will analyze what is being hit as drilling proceeds. Says Mankivsky: ''Schlumberger clearly has the best technology in the field.'' Recently Schlumberger enhanced its presence in seismic services with the acquisition of 51% of Prakla Seismos, a German seismic services company. Schlumberger has also been using its spare cash, currently about $1.5 billion, to buy drilling rigs at fire-sale prices. Notes Kenneth Miller, an analyst at Shearson Lehman Brothers: ''Schlumberger is building its earnings power, buying good assets at a discount.'' He expects the company to grow more than 20% per year for the next five years. Schlumberger recently traded for $60 on the Big Board, or 19 times estimated 1992 per-share earnings. That's still well below the premium P/E that the stock usually commands over the market multiple. Miller expects the shares to reach $75 within the next 12 months, and up to $100 within three years.