National Oilwell Varco Inc, the largest U.S. oilfield equipment provider, said orders fell by nearly a quarter in the first quarter and it expects demand for new offshore rigs to slow during the second half of the year. The company's shares fell about 7 percent. Demand for contract drilling is softening as rigs ordered during boom times are being delivered now. Large oil companies are tightening spending after a decade of double-digit increase in budgets as oil prices stagnate and project costs rise.