Oilfield services provider Halliburton beat analysts' expectations for earnings in the first quarter, even after oil prices declined.

Halliburton (ticker: HAL) earnings per share came in at 72 cents, compared with the analysts' consensus of 67 cents among those surveyed by FactSet. Revenue was $5.7 billion, compared with expectations for $5.5 billion.

Still, shares slipped 1.3% to $34.04 in premarket trading. Oil prices are more than 20% lower than a year ago. Higher crude prices encourage producers to invest in Halliburton's services. Falling oil prices do the opposite.

Nevertheless, the outlook for the year and longer term "is strong," CEO Jeff Miller said in a statement. "Our customers are clearly motivated to produce more oil and gas and service capacity is tight."