Two more oil-services firms have agreed to merge, this time in a deal that will see National Oilwell Varco ( NOV) acquire Grant Prideco ( GRP) for in excess of $7 billion. National Oilwell Varco pay $23.20 in cash and 0.4498 shares for each share of Grant Prideco. That values Grant Prideco's shares at $58 apiece, a 22% premium to the last close. When the transaction is completed, current stockholders of National Oilwell Varco will own about 86% of the combined company, and shareholders of Grant Prideco the rest. National Oilwell Varco said in a press release Monday that the transaction should add to its earnings and cash flow per share next year. The pact shouldn't affect Grant Prideco's pending sale of its tubular businesses to Vallourec S.A. The merger agreement was unanimously approved by each company's board, but Grant Prideco shareholders will have to clear it. The sides hope to close the deal late in the first quarter or early in the second quarter next year. Shares of Grant Prideco were gaining 18% to $56 in premarket trading. National Oilwell Varco was down 3.3% at $74.85.