Shares of National Oilwell Varco Inc. tumbled 4.6% in morning trade Friday, after the oil services company lowered first-quarter revenue expectations, citing the negative impact of lower oil prices on oilfield equipment demand. The company said it expects first quarter revenue of $1.94 billion, which is up from $1.80 billion a year ago but below the FactSet consensus of $2.09 billion. "The severity of the decline in demand for oilfield equipment resulting from the sharp fall in oil prices during late 2018, further compounded by capital austerity that has taken hold in upstream oil and gas markets, was greater than we expected," said Chief Executive Clay Williams. The company said that while market conditions have improved since the beginning of the year, and are expected to continue to improve throughout the year, the outlook remains "opaque." As a result, the company plans initiatives during the year to cut costs. The stock has gained 8.9% year to date, while the VanEck Oil Services ETF has soared 29.7% and the S&P 500 has rallied 15.9%.