HOUSTON (AP) — The oilfield equipment and services firm National Oilwell Varco Inc. says it will buy Robbins & Myers Inc. for $2.5 billion.

National Oilwell Varco will pay $60 per share for approximately 42.4 million shares of Robbins & Myers in an all-cash transaction. That gives Robbins & Myers shareholders a 28 percent premium based on Wednesday's closing price of $46.80. Shares jumped to $59.34 in premarket trading.

Both company boards have approved the transaction, but the deal requires approval by two-thirds of Robbins & Myers shareholders. Both companies are based in Houston.

Robbins & Myers makes and services pumps, valves and other equipment used to control the flow of oil and gas in drilling operations. National Oilwell Varco makes and services rigs, motors, bits, pipes and other drilling equipment.