Credit Suisse has reiterated its 'outperform' rating for oilfield services (OFS) group Petrofac, saying that the stock has been 'unfairly punished' after the cautious guidance given last week.Petrofac fell sharply on November 18th after saying that it expects "flat to modest growth" in net income in 2014 due to the rephasing of certain contracts.Credit Suisse said that the stock now trades on less than 10 times 2014 earnings with 30% upside potential to its target price of 1,535p. If it rolls valuations forward to 2015, the price-to-earnings ratio would be just 7.9 and the upside would rise to 57%."The European OFS sector has become widely disliked by equity investors, especially those who invest globally and favour US OFS players more geared to the shale plays," the bank said."But we argue this has opened up valuation gaps that present excellent opportunities to acquire stocks at levels which do not properly reflect the balance of risk and reward."Credit Suisse explained that while all seven OFC companies under its coverage have warned or guided lower on profits to one extent or another, these have been largely "self-inflicted" and some of the downgrades are not because of weak execution or increased competition."Petrofac remains a top pick, as we see last week's 18% share price drop as misinterpreting the message that profits are being deferred, not lost. We believe the underlying quality of Petrofac's earnings remain robust."Neither AMEC or Wood Group have profit warned per se, and this is reflected by sector outperformance year-to-date."Wood Group is rated 'outperform', while AMEC is labelled 'neutral'.Petrofac was trading 1.96% higher at 1,235.71p by 09:25 on Tuesday.BC