Energy services group John Wood Group said that fall-out from the oil spill in the Gulf of Mexico is not expected to materially affect the company's performance this year.The company disclosed that about 4% of the group's annual revenue is related to new deep water developments in the Gulf of Mexico.In an update covering the first half of the year the group said overall performance has been in line with expectations.The engineering division has performed as expected, with bidding volumes improving. This has increased confidence in a return to growth in 2011. The production facilities arm is seeing lots of activity in the North Sea while the division is also seeing an increasing level of international opportunities. The well support division is experiencing stronger activity in the US, and the good international performance should result in earnings before interest, tax and amortisation (EBITA) for the year coming in ahead of expectations. Things are less peachy in the gas turbine services and power solutions divisions, however."In Gas Turbine Services, we believe continuing maintenance deferrals by customers and lower activity in Power Solutions will contribute to a significant weighting to the second half and EBITA for the year below expectations," the company said.